In "The Gift of the Magi," the narrator tells us that the young couple's apartment had "a letter-box into which no letter would go and an electric...

As the story opens, we see Della counting her meager pile of coins, realizing that it's almost Christmas, and flopping onto the couch to cry. She's in her apartment, which she rents (she doesn't own it) and which includes furniture in the rent (meaning she doesn't own her furniture either).

While that's going on, the narrator describes the apartment for us, saying: 

"In the vestibule below was a letter-box into which no letter would go, and an electric button from which no mortal finger could coax a ring."

We already know that Della must be very poor, and now we find out that the letter-box is pretty much broken, and so is the doorbell. It sounds like maybe the lid of the letter-box is stuck, so you can't shove a letter into it; also, perhaps you can push on the button, but it won't make the ringing sound that it's supposed to. 

That makes sense: Della's in such poverty, so she probably can't afford to fix those things. She's not thinking about them, anyway; she's focused on how she can scrape up a little more money to get a Christmas present for her beloved husband.

What truth of human nature is presented in William Blake's poem "London"?

In "London," one of William Blake's "Songs of Experience," the depressing moral flaws of mankind are presented. The persona in the poem notes "marks of weakness" on every face. Given the qualities discussed in later stanzas, the weakness is likely moral, not physical, and therefore it leads to "marks of woe." The common note in the cries of men and babies, and in every voice and every proclamation is oppression--"mind-forg'd manacles." People are being victimized everywhere in the city. Even the Church, which should be a moral beacon, is darkened by the cruel poverty endured by the chimney sweeps because society is too selfish to provide a decent living for them. And the State, which could be a pillar of society, acts instead as a murderer of soldiers. Worst of all, the family unit is corrupted by immorality as a newborn baby is born blind because the father had contracted venereal disease and passed it on to his unknowing wife. Now their marriage is nothing more than a hearse to bear along their ruined relationship. This poem decries the moral darkness that plagues mankind and corrupts even the most central institutions of society.  

When the searchers from Poker Flat arrive at camp, what do they find?

Duchess, Piney, Oakhurst, and Tom are all that are left of the outcasts late in the story.  Uncle Billy ran off with the horses many days prior, and Mother Shipton starved herself to death, so that the other, younger, party members might survive.  John Oakhurst realizes that the only chance that the group has at survival is to request help from the very same town that cast them out.  He and Tom go part of the way together, but Oakhurst sends Tom the rest of the way by himself.  It is several days later before the Poker Flat rescuers arrive.  Their arrival is too late.  They find Duchess and Piney dead.  The two women are holding each other for warmth and have frozen to death, yet they look peaceful.  

And when pitying fingers brushed the snow from their wan faces, you could scarcely have told from the equal peace that dwelt upon them which was she that had sinned.

They found the body of Oakhurst a little bit away from the cabin.  He too was dead.  He had shot himself in the heart rather than succumb to the elements.  

And pulseless and cold, with a Derringer by his side and a bullet in his heart, though still calm as in life, beneath the snow lay he who was at once the strongest and yet the weakest of the outcasts of Poker Flat.  

I have been given the following essay topic: "In Frankenstein, the female characters are shaped as much by social expectations as by their own...

In Frankenstein, most of the female characters act according to social expectations of what women should do. This could be part of a larger feminist critique made by Shelley in the novel. You might notice that most of the female characters and all of the mothers are killed at some point in the novel, by illness or by violence. Mothers are strikingly absent in the novel, as this helps Shelley critique Victor's presumption in creating life on his own out of pieces of dead bodies, as he plays God and leaves the female body out of the equation. Note Victor's hesitation to build the female creature because he fears she and his original creature will "naturally" reproduce; this leads him to destroy the female creature before it is completely finished.

In the novel, Victor's mother, Elizabeth Lavenza, Justine, and Safie are the major female characters, and they exist mostly on the periphery of the story. Victor's mother dies early on, beginning the absent mother motif (later in the novel, the DeLacey family is without a mother, as well). Victor's mother, Caroline,  seems to be a fairly typical mother of the early 1800s; there isn't much evidence as to whether she "chooses" one action over another, but certainly becoming a wife and mother would have been expected of her by society. She seems to be warm and loving, and Victor has fond memories of her.

Elizabeth is like Victor's mother in some ways: she is meek and cheerful and maternal. She helps to nurse Mrs. Frankenstein in her illness and then basically takes her place in the family as caretaker once Caroline has died. Elizabeth later becomes a victim of the creature's violence due to Victor's destruction of the female creature he had promised his original creature. While she does choose to act as a mother figure to the Frankenstein family and she does choose to marry Victor, these actions are also in line with the expectations of her era.

Justine Moritz is probably the best example of a character who does not control her own fate. Justine is wrongly framed for the murder of Victor's younger brother William. The creature actually killed the child and planted evidence on Justine, who had been a loyal and beloved servant in the Frankenstein home. Clearly, her murder conviction (though unjust) is an example of how the character does not fit social norms for 19th century women, but she definitely does not have a choice here. The character who could have helped her was Victor, who knows the creature killed William, but he does not, and Justine is executed. Even if Victor had saved her, this act would be an example of the stronger male character rescuing the helpless female, which would align with social expectations for men and women.

Safie is the female character who perhaps makes the most decisive action when she chooses to leave Turkey to be with Felix DeLacey. She had previously been a slave and so was oppressed, like many women of the time, though more obviously so. Eventually she falls in love with Felix as he tries to help her father, and when her father later betrays the help given, she chooses to leave him to be with Felix. This is a choice, but it is a choice between two men who will provide protection for her, so it's still somewhat traditional as far as gender norms go.

Most of the evidence in the novel suggests that female characters are less shaped by their own choices than by social expectations for women. 

In geography, what is a mesa?

The word mesa is derived from the Spanish word for tabletop. The word is used in geography to describe a specific type of landform. These landforms, named mesas by the early Spanish explorers because of their table like appearance, are mountains, or hills, that have a large flat top region and have developed steep sides, which in many cases are cliffs. They get their form from water erosion over many years washing away the softer rocks located around the sides of the structure, while harder rock, making up the top of the structure, remains present. In most cases, a mesa is found in a dry climate, which allows rock layers to develop in a horizontal manner allowing the flat top to form. Currently, the largest mesa in the world is considered to be the Grand Mesa located in the state of Colorado in the United States.

Hope this helps!

What are some examples of bacteria, fungi, viruses, and parasites?

Bacteria are prokaryotes.  Their cells do not include a nucleus or membrane-bound organelles.  Many species of bacteria can be put into one of two groups, Gram positives and Gram negatives, based on their cell wall structure.  Gram positive bacteria have many layers of peptidoglycan in their cell walls and include common bacteria like Staphylococcus aureas, Streptococcus pneumoniae, Bacillus anthracis, Lactobacillus acidophilus found in yogurt, and Chlostridium botulinum.  Gram negative bacteria have fewer layers in their cell wall and have an extra membrane surrounding their cell wall.  Gram negatives include E. coli, Psuedomonas aeruginosa, Proteus mirabilis, Enterobacter aerogenes, and Neisseria gonorrhoeae.  

Fungus includes both yeast and mold.  One common yeast is Saccharomyces cerevisiae.  It is used to make bread and alcoholic beverages.  Molds include Rhizopus spp., Aspergillus spp., and Penicillium spp.  

Viruses are obligate intracellular parasites, which means that they cannot reproduce outside of a host cell.  Viruses include varicella-zoster virus (chicken pox and shingles), HIV (AIDS), herpes simplex virus (cold sores and genital herpes), human papilloma virus (warts), and bacteriophages, which infect bacteria.

Parasites are organisms that live in or on a host and benefit from it while causing harm to the host (optimally) without killing it.  Entamoeba, Giardia, Plasmodium, flukes, tapeworms, ticks, fleas, and lice are all considered to be parasites.

Who is Hillary Clinton and where does she stand on important political issues?

Hillary Diane Rodham Clinton  was born on October 26, 1947 in Chicago and raised in Illinois. She was raised in a Republican family, and was politically active even as a high school student, but during her years as a student at Wellesley College, began to shift towards the Democratic party, a position she has maintained throughout her adult life. In college, she became active in supporting the movement against the Vietnam War and became involved with the Civil Rights Movement. She graduated in 1969 with departmental honors and enrolled in Yale Law School, where she met Bill Clinton (her soon to be husband). She graduated from law school in 1973. During her time at Yale, she began her work on children's issues, including serving as a lawyer for the Children's Defense Fund.

Moving to Arkansas with her husband Bill Clinton, Hillary Clinton continued to practice as a lawyer, teach law, and work on advocacy projects, especially those benefiting children, including being part of such organizations as Arkansas Advocates for Children and Families, and Arkansas Children's Hospital, Legal Services, and the Children's Defense Fund. When her husband became President, Clinton continued to take an active role in politics, including advocating for health care reform. 

After the end of her husband's two-term presidency, Hillary Clinton was elected United States Senator from New York in 2000 and served two terms. In 2008 she ran against Obama for President in the Democrat primaries; although she did not succeed in being nominated, she served the Obama administration as U.S. Secretary of State from 2009 to 2013. With her return to private life in 2013, she continued to advocate for women's and children's rights as well as writing her memoirs and becoming a popular lecturer. On April 12, 2015, she formally became a candidate for the Democratic nomination for President.

Her political positions are usually described as mainstream center left, advocating for gradual change based on a technocratic approach to policy and a belief in making necessary compromises to get legislation passed.  

Clinton supports for equality for minorities, women, and members of the LBGT community. She wants to improve the Affordable Care Act to make insurance increasingly affordable and accessible and ensure adequate parental and medical leave for all workers; she believes that all people have the right to adequate medical care. She supports a federal minimum wage increase to $12 per hour. Clinton supports immigration reform and education reform. In foreign policy, she is moderately hawkish, believing that the United States must stay engaged with the rest of the world but work multilaterally rather than unilaterally. She wants to act to moderate climate change, improve infrastructure, and reduce gun violence in the United States. 

What is poisoning?

Causes and Symptoms

Probably the most accurate statement that can be made about the occurrence of poisoning in the United States is that the numbers vary widely depending on the information source and definition of poisoning. Incidents can be grouped into intentional poisonings, accidental poisonings, occupational and environmental poisonings, social poisonings, and iatrogenic poisonings. There is no single organization that collects and analyzes data from hospitals, physicians’ offices, police and court records, and industrial accident and exposure records. One source has reported that as many as eight million people are accidentally or intentionally poisoned each year. It has been stated further that 10 percent of all ambulance calls and 10 to 20 percent of all admissions to medical facilities involve poisonings.

Many incidents of poisoning go unreported because a poison control center is not consulted or the effects are not severe enough to require extensive medical treatment. In other cases where exposure to the toxic agent involves constant contact to low but toxic levels of industrial chemicals, such as occupational or environmental exposures, symptoms may be subtle or confused with diseases that are associated with the normal aging process. The degree of illness and/or the number of premature deaths resulting from environmental exposure to naturally occurring or artificial toxic substances—radiation, chemical waste, and other toxins in the air, water, and food supply—is simply not known.

The most consistent and reliable sources of information on accidental poisoning in the United States are the annual statistics compiled by the American Association of Poison Control Centers. While poison control centers receive some calls related to intentional poisonings, 88 percent of the calls are considered accidental exposures. Combining all the poisoning types together, poison control centers are called concerning about 2.2 million human cases each year. It is important to note, however, that extrapolations from the number of reported poisonings to the number of actual poisonings occurring annually in the United States cannot be made from these data alone.

About 93 percent of exposures occur in the home, more than half involve children under six, and three-fourths involve ingestion. The great predominance of young children in the accidental poisoning category reflects the inquisitive behavior of that age group. For children under the age of one year, inappropriate administration of medications by the parents is the dominant cause of poisonings. For children over the age of five, exposure to toxic substances often represents the simple misreading of a medication label or the manifestation of family stress or even suicidal intent. These children have increased incidence of depressive symptoms and family problems compared to their nonpoisoned peer group.

Intentional poisoning of children also occurs—usually as a well-planned act of a psychologically disturbed parent. Although many of these incidents are clearly homicidal and abusive by design, some have received medical notoriety as cases of Münchausen syndrome by proxy.
Münchausen syndrome itself is a psychiatric disorder in which the patient achieves psychological comfort from the attention and treatment received under the pretense of being afflicted with a serious or painful illness. In a variation of this condition, the psychiatric needs of an adult are fulfilled through an induced medical disorder in the child. For example, a parent might surreptitiously administer syrup of ipecac to his or her child, inducing unexplained vomiting and gastrointestinal disorders that requires extended hospital care. The phenomenon is rare but well documented in the medical literature and is classified as a form of child abuse.

Intentional poisonings are mostly suicide-related. The Centers for Disease Control and Prevention (CDC) reported that more than 38,000 Americans killed themselves in 2010. Of all suicides from 2005 to 2009, poisoning was the method chosen by almost 40 percent of women and about 12 percent of men. Although carbon monoxide (as in motor vehicle exhaust) is one of the most common agents used, intentional dosing with large quantities of drugs is also very frequently involved. Of the many thousands of drugs that could be used for overdose incidents, 90 percent of actual cases involve only about twenty products in nine drug groups. Most of these are addictive or abused drugs, including stimulants, antidepressants, tranquilizers, narcotics, sedatives or hypnotics, and antipsychotics. Alcohol alone is seldom lethal but is often consumed along with the more deadly drugs and may make the lethal effects possible.

Social poisoning is related to drug use or abuse, which can have significant societal consequences. There are hundreds of thousands of hospital and emergency room admissions each year for overdose treatment as well as for the indirect consequences of recreational drug use, such as violent crime, trauma, and vehicular accidents. Almost 400,000 drug-abuse-related emergency room visits were projected to have occurred in 1990 by the Drug Abuse Warning Network (DAWN), a federal government-sponsored data collection system. These figures do not include alcohol, however, unless it is mentioned as having been involved in a mixed drug exposure event.

The abuse of alcohol, the most widely available chemical intoxicant legally allowed for recreational use, is a major social problem in the United States. While a majority of the alcohol-consuming public demonstrates a lifelong pattern of little or moderate drinking without the development of addiction-related problems, it has been reported that a small percentage of the population (5 percent to 10 percent) drinks between one-third and one-half of all alcohol consumed. The causes of
alcoholism involve a complex interaction of social, physiological, and genetic risk factors. In the United States, there are approximately 9 million people classified as chronic alcohol abusers, and according to the CDC, about 80,000 deaths per year are attributable to alcohol-related causes.

Tobacco use, although not as closely associated with criminal behavior and vehicular accidents as drugs and alcohol, has been connected with increased incidence of cancer, respiratory illnesses, and cardiovascular diseases. According to the World Health Organization, more than 5 million deaths worldwide per year are attributable to tobacco use. Both smoking and excessive alcohol consumption are becoming increasingly less socially accepted, but the continued wide acceptance of both alcohol and tobacco use obscures their potential to poison.

Treatment and Therapy

Emergency medical treatment of the poisoned patient is most often based on the relief of symptoms and the provision of life support. If the patient is awake and alert, a medical history is taken and a clinical examination is performed, both of which can help determine substance exposure. The medical staff must never assume that the patient is providing truthful information, especially if clinical impressions conflict with the patient account. If the patient is comatose, then stabilization and life support take immediate priority over determination of the specific toxic substance involved. The attending physician will want to prevent airway blockage and to maintain respiration and circulation, which may require mechanical aids for breathing assistance. Treatment of cardiac and blood pressure problems can be accomplished with drugs, fluid, or oxygen administration. If the patient is unconscious, the depth of central nervous system
depression can be evaluated using a standard test of reactivity to light, sound, pain, and the presence or absence of normal body processes. If the patient is suffering from seizures, drugs that counteract these symptoms can be administered.

Although many hospitals offer in-house toxicology
testing in a clinical laboratory, treatment usually must begin before results are available. For this and several other reasons, a comprehensive toxicology testing laboratory is not as useful an asset in the emergency treatment of poisoning as might be assumed. It would be impossible for any analytical laboratory to provide timely or cost-effective emergency identification of all potentially toxic substances. Instead, a more efficient strategy concentrates on analyzing those substances for which a specific antidote exists or for which specific medical procedures are required in a critical period of time. A very high percentage of drug overdose cases involve one of a group of six or eight drugs that will vary depending on locality. Pesticide poisoning, for example, is a more prevalent medical problem for rural than urban hospitals. Drug abuse is a problem in all localities, but the frequency and type of drugs abused vary. Regional preferences exist for PCP, cocaine, amphetamines, and opiates. Even prescription drug abuse depends on locality and the patient population.

Common pain relievers found in virtually every home medicine cabinet constitute a large number of both adult and pediatric poisoning incidents. Preparations containing aspirin, as well as nonaspirin analgesics containing acetaminophen (such as Tylenol), are possibly life-threatening when consumed in excess. Acetaminophen poisoning is particularly insidious since death from total and irreversible destruction of the liver will occur unless the antidote, a chemical called acetylcysteine, is administered within six hours of ingestion of a lethal dose. Since a specific antidote exists, most hospitals with emergency service will offer around-the-clock testing for acetaminophen levels in the blood. Aspirin, although not as lethal as acetaminophen, can be fatal if a sufficient amount is consumed. Its universal availability and common usage make aspirin a significant poisoning agent encountered in all localities. The symptoms of toxicity are related to aspirin’s effects on temperature regulation, rate of breathing, and the body’s ability to influence the acidity of the blood. Treatment involves monitoring the patient’s vital signs and calculating the severity of the dose taken. Vomiting may be induced with syrup of ipecac, or charcoal (a very active adsorption agent) may be given orally to limit gastric absorption. Intravenous fluids may also be given to counteract the blood acidity changes.

Prescription drugs that are commonly overused or abused (antiepileptic medication, sedatives and tranquilizers, and antipsychotic or antidepressant drugs) are often routinely assayed in the hospital laboratory as part of the treatment process for patients receiving these medications. The levels in the blood can be monitored to determine the toxicity status of the patient. Usually, supportive care is sufficient for treatment until the drug clears the system. For certain tranquilizers and antidepressants, an antidote called flumazenil can be administered, but it must be used with caution.

Poisoning from an overdose of opiates or morphinelike drugs is a special treatment case. A specific antidote called naloxone can be administered if the patient is treated before irreversible respiratory depression occurs. Recovery is virtually instantaneous and dramatic, with a comatose patient becoming alert within seconds of naloxone administration. For this reason, the routine treatment of comatose patients includes the administration of opiate antidote even when the cause of the unconscious state is unknown.

Although heavy, long-term ethyl alcohol use invariably leads to liver dysfunction and a number of other organ disorders, alcohol is not usually life-threatening unless it is consumed in quantities sufficient to cause a coma. Death most commonly results from respiratory depression and related complications. Other types of alcohols, as well as antifreeze, can be involved in both accidental and intentional poisonings. Methanol or wood alcohol is a common industrial solvent found in materials around the home or work site; consumption can cause blindness and death. Isopropyl alcohol (or rubbing alcohol), although not as toxic as methanol, can also cause severe illness and death when consumed in sufficient quantities. Ethylene glycol, a common ingredient in antifreeze, is highly toxic and is especially attractive to small children and pets because of its sweet taste. It may also be consumed by alcoholics as an ethanol substitute. When not treated, its consumption can result in kidney failure. It is not the alcohols themselves that are the primary toxins but the degradation products called metabolites that form in the body in an attempt to eliminate the foreign substance. Ironically, the treatment for both methanol and ethylene glycol poisoning is administration of high doses of ethanol, which prevents the formation of toxic metabolites by the liver.

In the United States,
lead poisoning is a major medical problem for children living in older, substandard housing; they can become exposed to large amounts of lead from the consumption of lead-based paint. (Even though such paints are no longer used in residential housing, many older buildings remain contaminated.) Another major source of exposure is inhalation of leaded gas fumes and exhaust. Other less common sources of lead poisoning include the consumption of food stored in leaded crystal or pottery or moonshine whiskey distilled in automobile radiators. Intentional gasoline sniffing by adolescents can also be a problem. Lead exposure is extremely hazardous because its effects are both severe and cumulative. Children are especially susceptible to lead poisoning because they absorb and retain more of this substance and have less capacity for excretion than adults.

The nervous system is a major site for lead toxicity, causing both psychological and neurologic impairment. The blood cell production can also be affected, with resulting anemia and decreased oxygen-carrying capacity. Because lead toxicity can result in behavioral and learning disorders that may already afflict children living in substandard conditions, sometimes poisoning cannot be detected by clinical symptoms alone and must be diagnosed through blood testing. Test data indicate that the level of lead associated with nervous system disorders is probably lower than previously believed. In the United States, a major screening effort has been financed by the federal government to detect high lead body deposits in children. The goal is to find affected children and to treat them before permanent damage occurs.

Perspective and Prospects

Poisoning has been a medical problem since the earliest times of human history. A tremendous variety of poisonous substances can be encountered in the natural world alone. It has been estimated that 200,000 plants and animals are known to be toxic to humans, some organisms producing as many as fifty or sixty toxins. The potential of almost any substance to be poisonous was recognized during the Renaissance by Paracelsus, a founder of modern toxicology, who stated, “All substances are poison; only the dose makes something not a poison.” Many folk remedies and tribal medicine practices were derived from centuries of trial-and-error experiences with toxic plant and animal species in the environment. Historically, the development of the sciences of pharmacology and toxicology is closely related to the study of poisons.

As societies become more urban and technology-based, poisoning problems shift away from natural toxin exposures to those related to drugs and industrial chemicals. For many of these types of poisonings, sustaining the vital life processes until the toxin is cleared from the body is the only method of treatment. Specific antidotes are not available for many drugs or even for many natural poisons. Since a large number of toxins critically affect the nervous system, a diagnostic and treatment system has been developed based on the “toxidrome” concept. If a specific area of the nervous system can be shown to be affected, treatment can begin to counteract those effects even if the identity of the toxin is not known.

The symptoms of acute poisoning or overexposure to a toxic agent are likely to be treated as individual medical problems by physicians in an emergency medicine environment. Meanwhile, social poisons, which often do not create immediate medical emergencies, continue to exact enormous economic and medical costs to society over the long term; these poisoning problems have not been dealt with successfully by social, medical, or governmental agencies. In the case of environmental toxins, little if any well-established information on the long-term toxicity of these substances is available. The science of toxicology, particularly with regard to establishing the risk of exposure of a population to environmental toxins, often becomes a guessing game played by a governmental regulatory agency. Until societal and environmental poisonings can be better evaluated and controlled, they will continue to constitute serious economic and quality-of-life problems.

Bibliography

Baselt, Randall C. Disposition of Toxic Drugs and Chemicals in Man. 9th ed. Foster City, Calif.: Biomedical, 2011.

Dart, Richard C., ed. Medical Toxicology. 3d ed. Philadelphia: Lippincott Williams & Wilkins, 2004.

Garriott, James C., ed. Medicolegal Aspects of Alcohol Determination in Biological Specimens. Littleton, Mass.: PSG, 1988.

Klaassen, Curtis D., ed. Casarett and Doull’s Toxicology: The Basic Science of Poisons. 8th ed. New York: McGraw-Hill, 2013.

Morgan, Monroe T. Environmental Health. 3d ed. Belmont, Calif.: Thomson/Wadsworth, 2003.

"Poisoning." MedlinePlus, August 30, 2013.

Timbrell, John. Introduction to Toxicology. 3d ed. Washington, D.C.: Taylor & Francis, 2003.

Warren, Christian. Brush with Death: A Social History of Lead Poisoning. Baltimore: Johns Hopkins University Press, 2001.

What is severe combined immunodeficiency syndrome (SCID?

Causes and Symptoms

Severe combined immunodeficiency
syndrome (SCID) is a genetic defect in which one of several genes involved in the immune system has a mutation that either prevents gene expression or causes the production of faulty products. The most common cause of SCID, accounting for about half of cases, is mutations in the X-linked gene IL2RG, which codes for the third chain of the interleukin-2 (IL-2) receptor, and also a part of several other interleukin receptors. Interleukin receptors are proteins embedded in the plasma
membrane of cells in the immune system
that interact with interleukin molecules, which carry important immune system signals. This type of SCID is called X-linked combined immunodeficiency (XCID), and the faulty interleukin receptors
prevent the development of Tdf cells and natural killer (NK) cells, both of which are required to prevent infections successfully. Because XCID is an X-linked defect, it is much more common in males.

The remaining cases of SCID are attributable to mutations in many different genes, with new defects being discovered every year. The types of genes involved range from those that code for proteins that interact with interleukin receptors and enzymes involved in purine metabolism, to genes that code for enzymes involved in antigen
receptor production. In addition, a variety of lesser known defects and some genetic disorders show some, but not all, of the symptoms of SCID.

The most common of the remaining defects, accounting for about 20 percent of cases, is deficiency in the enzyme adenosine deaminase (ADA), which is involved in purine metabolism. This form of SCID, called ADA SCID, results in the accumulation of a toxic form of adenosine that especially affects lymphatic tissue. No T or B cells are produced. Deficiency in another enzyme, purine nucleoside phosphorylase (PNP), although much rarer, acts in a similar fashion.

Regardless of the underlying causes, symptoms are similar for most types of SCID. The overwhelming clinical symptom is problems with repeated, persistent infections that do not respond to standard treatment. Severe infections such as meningitis or septic arthritis may occur. Infections with opportunistic pathogens such as Pneumocystis carinii also frequently occur. Symptoms of graft-versus-host disease
(GVHD) may occur in infants because of lymphocytes received from the mother or in patients following blood transfusion. A chest x-ray typically shows lack of a thymic shadow, indicating that the thymus has not developed properly. There is often also a family history of immunodeficiency and infant deaths caused by serious infection.

Treatment and Therapy

Left untreated, most infants die within the first year, so rapid identification of the symptoms is extremely important. Prenatal diagnosis is possible and is recommended in families with a history of SCID or similar problems. If SCID is detected early enough, then several treatment options are available, even potential prenatal treatment.

For the majority of SCID cases, bone marrow
transplantation

is the standard treatment. To prevent GVHD, either the marrow must come from an identical twin or it must be depleted of T cells prior to transplantation. Although a close genetic match has the highest success rate, unmatched and T cell–depleted marrow can be used if matched marrow is unavailable. A survival rate of more than 90 percent has been accomplished when the marrow is from a parent or full sibling. It has typically been routine to use chemotherapy to kill the recipient’s bone marrow before transplanting donor marrow, but in the case of SCID patients this has been found unnecessary (and seems to lower the survival rate) because the recipient has no T cells to cause rejection.

When transplantation is successful, donor stem cells present in the marrow populate the recipient’s marrow and establish a functioning immune system. Unfortunately, some residual GVHD may occur, and over time T cell function seems to diminish in many cases, in spite of apparent initial success. The reasons for the latter problem are unknown.

Although transplantation may also work for ADA SCID, an alternative is polyethylene glycol (PEG)-bovine ADA replacement therapy. This treatment must be administered on an ongoing basis by frequent intravenous injections of PEG-ADA to maintain appropriate enzyme levels. Unfortunately, PEG-ADA is not always available and is extremely expensive, leaving transplantation the only option in some cases.

Still in the experimental stage is gene therapy
to replace the defective genes. Experiments on this approach began in the early 1990s, and although the first attempts at curing ADA SCID showed partial success, the patients still required continued treatment with PEG-ADA. Since then, efforts have focused on better ways to insert the correct genes into the patient’s own stem cells. Stem cells from the bone marrow must be isolated, treated, and then returned to the patient.

The most promising results came from experiments begun in 1999 involving gene therapy for XCID. Following the procedure, the infants developed apparently normal immune systems. Unfortunately, by the summer of 2002 one of the boys developed leukemia, and another developed it by the end of the same year. Some trials were stopped as a result. The apparent cause of the leukemia was insertion of the gene at an inappropriate location, a concern expressed early in the discussion of gene therapy for this disease. Gene therapy still holds great promise, but more work needs to be done to ensure its long-term safety and effectiveness.

Bibliography:

Blaese, Michael R., et al. “T Lymphocyte-Directed Gene Therapy for ADA SCID: Initial Trial Results After Four Years.” Science 270 (October 20, 1995): 475–480.

Cohen, Philip. “Fresh Blow for Gene Treatments as Safety of a Second Virus Is Questioned.” New Scientist 178 (June 7, 2003): 17.

Cooper, Max D., et al. “Immunodeficiency Disorders.” Hematology 2003, no. 1 (January 1, 2003): 314–330.

Hawley, Robert G., and Donna A. Sobieski. “Of Mice and Men: The Tale of Two Therapies.” Stem Cells 20 (2002): 275–278.

MedlinePlus. "Immune System and Disorders." MedlinePlus, May 21, 2013.

National Human Genome Research Institute. "Learning about Severe Combined Immuodeficiency (SCID)." Genome.gov, October 3, 2011.

Schwarz, Klaus, et al. “Human Severe Combined Immune Deficiency and DNA Repair.” Bioessays 25, no. 11 (November, 2003): 1061–1070.

Scollay, Roland. “Gene Therapy: A Brief Overview of the Past, Present, and Future.” Annals of the New York Academy of Sciences 953 (2001): 26–30.

How does Prosper spend the money Barbarossa gives him? What types of things does he feel are necessary and unnecessary?

We can find these answers in Chapter 6: "A Nasty Coincidence." Barbarossa has paid off the kids for their hawked items, and they're feeling suddenly very rich. But we know that Prosper is a very realistic and careful person.

So, Prosper spends the money on practical, useful things, and not on fun, silly things.

To Prosper, necessary things are items like basic food, warm jackets, and sturdy shoes to keep the kids alive, safe, and comfortable through the cooler weather. He's always thinking about practical ways to keep himself, Bo, and the other kids safe and fed, and he doesn't think it's a good idea to waste the money on silly stuff.

Speaking of silly stuff, to Prosper, unnecessary things are items like fancy cakes dusted with sugar and wrapped up in delicate paper, as well as the TV that Riccio wants, or the toys that Prosper and Bo sold so that they could earn money for food. Prosper understands that items like these, while normal in a typical household with children, are just not a necessity to kids like them who are trying to make it on their own without a home.

To sum that up, Prosper understands what's necessary to life (basic food and clothing) and that anything else is just not needed (like fancy food and items that simply entertain). He knows that the money they earned from Barbarossa must last a long time and can't be wasted on things that the kids would like to have for fun. Considering these questions, then, helps us understand how serious and thoughtful Prosper is as a character, and how Riccio is quite different from him.

What are two possible reasons that the United States became an imperial nation in the late 1800s?

There were many reasons why the United States became an imperial nation in the late nineteenth century. Perhaps the two most important reasons were as follows. 

First, the United States sought markets around the world for its manufactured goods. There was a real fear in the United States and other industrialized nations that the country's economy might fall prey to overproduction--its factories, in other words, might produce more than domestic markets could bear. So American business leaders sought to expand their interests overseas, and pushed the government to adopt policies that protected their rights to trade. The so-called "Open Door" notes, which claimed the right of the United States to trade alongside other nations in China, was an example of this motive in practice. 

Another reason was that many perceived that the United States needed to expand its military influence around the world, especially in the Pacific. This motive went hand in hand with the commercial motives discussed in the preceding paragraph. The United States sought islands in the Pacific as naval bases that could extend its reach into Asia and protect its access to markets in that region. For both of these reasons, the United States emerged as a major imperial power after crushing Spain in the Spanish American War of 1898. 

What is syphilis?

Causes and Symptoms

Syphilis is a sexually transmitted disease (STD) resulting from infection by Treponema palladum. The history of the disease is unclear. Evidence exists that its origin may have been linked with a disease, yaws, found in the Western Hemisphere at the time of explorer Christopher Columbus (1451–1506). Yaws is a relatively mild disease generally transmitted through contaminated objects or open skin
lesions, but not generally through sexual transmission; it results from infection by a subspecies of Treponema called T. palladum ssp. pertenue. The theory suggests that this may have been the form of the disease brought back to Europe on one of Columbus’s ships. Mutation and sexual transmission in the population of Europe may have produced the more serious form of the disease.

The disease is characterized by several distinct stages. Initial exposure to the organism during sexual intercourse results in formation of a painless skin lesion called a chancre at the site of infection (primary syphilis), developing anywhere from a week to months after infection. Spirochete
bacteria may be isolated from the lesion, as well as being found live inside white blood cells (macrophages and neutrophils) that infiltrate the area. The white cells may be a mechanism for systemic spread of the organism. The lesion generally heals spontaneously, leaving the impression that the disease has been eliminated.

During the weeks after formation of the chancre, the spirochetes multiply to large numbers and become disseminated throughout the body. A second stage (secondary syphilis) often appears within two months following regression of the chancre. Symptoms are often described as flu-like, with malaise, headache, fever, and joint aches. A skin rash often appears, covering most of the body. Sores may develop in the mouth and throat and on many of the mucous membranes in the body. The organism is highly transmissible during this period. The rash and other symptoms generally fade over a period of weeks.

Approximately 10 percent of untreated cases develop a third, or tertiary, stage of syphilis. The organism can infiltrate any organ or system in the body, resulting in soft tumors (gummas) in the eyes, lungs, bone, brain, or other organs. Symptoms are characteristic of the organ infected. For example, infection of the brain or other areas of the central nervous system are described as neurosyphilis or syphilitic dementia, characterized by memory loss, personality changes, and neurodegeneration. Even if tertiary syphilis is treated, prognosis for the patient at this stage is often poor.

Treponema has the ability to cross the placenta, and the infection of a pregnant woman may result in congenital syphilis, or infection of her unborn child. Infection may kill the fetus or cause it to be born with obvious deformities such as blindness or physical abnormalities. The infant may also be asymptomatic. An undiagnosed infection will likely progress, with symptoms appearing within weeks after birth. It is common for a rash to appear, with evidence of tertiary stage neurosyphilis or cardiovascular syphilis.

A diagnosis of syphilis can be made through microscopic examination of lesion exudates, noting the presence of spirochetes. However, Treponema is notoriously unstable, and the test must be made shortly after obtaining the specimen. More commonly, diagnosis is based upon serological testing for serum antibodies against the organism or tissue lipids released from infected or damaged cells.

Treatment and Therapy

Penicillin is the preferred method of treatment for both primary and secondary syphilis. If the disease has progressed to the tertiary stage, then antibiotic treatment will still eliminate the organism, but it will not reverse organ damage that may have occurred. Treatment for related organ involvement is symptomatic.

Alternative antibiotics include erythromycin, tetracyclines, and chloramphenicol, if necessary. However, only penicillin is effective during the tertiary stage or for use in pregnant women.

Perspective and Prospects

Despite the long-time existence of effective therapy, penicillin or alternative antibiotics, and the absence of any reservoir for T. palladum other than humans, syphilis remains the third most common sexually transmitted bacterial disease in the West. Only gonorrhea and chlamydia are more common.

As a result of effective therapy and the generally obvious symptoms of the disease, tertiary syphilis has largely disappeared. However, sexual practices continue to sustain spread of the disease. The Centers for Disease Control and Prevention estimate that 55,400 people acquire new syphilis infections each year in the United States. Three factors are primary contributors to the resurgence of the disease: prostitution, the increase in riskier sexual practices among homosexual men, and general apathy toward a disease that is relatively easy to treat in its early stages. An increase in congenital syphilis also reflects the presence of the disease in women of childbearing years. In the absence of condom use, both unwanted pregnancy and the spread of STDs such as syphilis may result.

No vaccine currently exists for syphilis. The inability to culture the organism in the laboratory has made research related to Treponema difficult, and the organism does not infect animals other than humans to act as a method of vaccine production. However, genetic engineering has resulted in the cloning of several bacterial gene products related to surface proteins and virulence factors, allowing the possibility for a vaccine in the future. For now, the best means of controlling syphilis remains the prevention of its spread through education and safer-sex practices, as well as early treatment of those infected.

Bibliography

Centers for Disease Control and Prevention. The National Plan to Eliminate Syphilis from the United States. Atlanta: U.S. Department of Health and Human Services, 2006.

Centers for Disease Control and Prevention. "Syphilis—CDC Fact Sheet." Centers for Disease Control and Prevention: Sexually Transmitted Diseases (STDs), February 11, 2013.

Mandell, Gerald L., John E. Bennett, and Raphael Dolin, eds. Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases. 7th ed. New York: Churchill Livingstone/Elsevier, 2010.

Murray, Patrick R., Ken S. Rosenthal, and Michael A. Pfaller. Medical Microbiology. 7th ed. Philadelphia: Elsevier/Saunders, 2013.

Parker, James N., and Philip M. Parker, eds. The Official Patient’s Sourcebook on Syphilis. ICON Group, 2009.

Scholten, Amy. "Syphilis." Health Library, May 16, 2013.

Quetel, Claude. The History of Syphilis. Baltimore: Johns Hopkins University Press, 1990.

Sutton, Amy L., ed. Sexually Transmitted Diseases Sourcebook. 3d ed. Detroit, Mich.: Omnigraphics, 2006.

Does Johnsy's doctor think that she will recover from her illness, and does Johnsy plan on getting better in "The Last Leaf"?

Johnsy, one of two aspiring artists who live in Greenwich Village has contracted pneumonia because before coming to New York, she has lived in sunny California. Weakened and depressed, Johnsy has given up hope of getting well.

After a doctor examines Johnsy, he tells her roommate named Sue that Johnsy has, perhaps, a one in ten chance of surviving. Then, he asks if Johnsy has any goals or anything for which she truly wants to live--a man, perhaps?  If so, he can lower the odds to one in five. Sadly, Sue informs the doctor that Johnsy is not in love, nor does she have any strong passion for anything.

“Well, it is the weakness, then,” said the doctor. “I will do all that science, so far as it may filter through my efforts, can accomplish.

So, the doctor does not have much hope. As the despairing Sue watches over her friend, Johnsy awakens and tells Sue that she has been watching the ivy outside the window and counting the leaves as they have fallen.

When the last one falls I must go, too. I've known that for three days. Didn't the doctor tell you?”

Sue contradicts her, saying that the doctor has said that she has a strong chance of getting well. But, of course Sue is really worried about what the doctor has told her and because of this, she hurries to the apartment of Mr. Behrman and tells him about Sue. Because he cares greatly about Sue, he is very concerned. In fact, he loves the young woman like a daughter. Thus, he paints an ivy leaf on the window in the night so that Sue will not let herself die. And, it is only the sight of the ivy leaf painted by poor Behrman who himself dies of pneumonia that encourages Sue the next night to fight for her life.

What is quadriplegia?

Causes and Symptoms

Quadriplegia may result from spinal cord injury, especially in the area of the fifth to seventh cervical vertebrae. Such injury usually follows trauma or vertebral pressure on the soft tissue of the cord. Damage causes flaccidity in the arms and legs, as well as loss of power and sensation below the level of injury. Spinal cord injuries above the fifth cervical vertebra dramatically affect other body systems as well.

For example, cardiovascular complications result from a block in the sympathetic nervous system that allows the parasympathetic system to dominate. One possible complication is hypotension (blood pressure below 90/60) resulting from vasodilation, which allows blood to pool in the veins of the extremities and thereby slows the venous blood return to the heart. Another complication is low body temperature (96 degrees Fahrenheit or lower) from the inability of blood vessels to constrict efficiently, allowing constant close blood vessel contact with the body surface and consequent heat loss. Bradycardia (slow heart rate) may occur from stimulation of the heart by the vagus nerve and absence of the inhibiting effects of the sympathetic system. A decrease in peristalsis, the movement of food through the gastrointestinal system, results from various types of shock. Respiratory complications, a major cause of death, may occur from damage to the upper cervical cord. Autonomic dysreflexia may occur in injuries above the fourth thoracic vertebra, in which a severed connection between the brain and the spinal cord produces an exaggerated autonomic response to such stimuli as distended bladder, fecal impaction, infection, decubitus ulcers, or surgical manipulation. The key symptom of autonomic dysreflexia is hypertension (high blood pressure).

A complete physical and neurologic examination must assess remaining motor function and determine if the cord injury is complete or partial. Detailed information about the trauma may help health care providers anticipate other related injuries. Computed tomography (CT) scans can identify fractures, dislocations, subluxation, and blockage in the spinal cord. X-rays of the head, chest, and abdomen can rule out underlying injuries. Since this type of injury has such far-reaching physiologic effects, significant laboratory data assessing respiratory, hepatic (liver), and pancreatic functions are necessary to provide a baseline.

Treatment and Therapy

The treatment of quadriplegia begins at the scene of the accident, with immobilization of the neck and spine. At the hospital, methods of immobilization include insertion of Gardner Wells tongs or halo traction. A turning frame helps prevent pulmonary complications such as atelectasis (partial lung collapse), pneumonia, and pulmonary embolism; cardiovascular complications such as blood clot formation and orthostatic hypotension; and other complications such as kidney stones, muscle atrophy, decubitus ulcers, and infections.

After stabilization, therapy consists of steroids, intravenous glycopyrrolate to maintain the integrity of the gastrointestinal tract, insertion of a Foley catheter, and administration of a potent diuretic such as mannitol. This treatment regimen is followed for ten days to decrease spinal cord edema (swelling). Unchecked edema further compromises the blood supply to sensitive cord tissue, producing irreversible cord damage. Prevention of ascending cord edema preserves higher cord segments and maximum function in the upper extremities. Each cord segment preserved means greater potential for rehabilitation.

After ten days of therapy, surgical fusion stabilizes the unstable spine. Surgery must also remove bone fragments that can irritate the spinal cord and, in later stages, aggravate spasticity. Another necessary part of treatment is aggressive respiratory therapy that, in the intubated patient, includes instillation of three to five milliliters of normal saline solution and bagging the patient before thorough suctioning to remove secretions and prevent mucus plugs. In cervical cord injuries above the fifth vertebra, intubation and ventilator assistance are always necessary.

Bibliography

Asbury, Arthur K., et al., eds. Diseases of the Nervous System: Clinical Neuroscience and Therapeutic Principles. 3d ed. New York: Cambridge University Press, 2002.

Berczeller, Peter H., and Mary F. Bezkor. Medical Complications of Quadriplegia. Chicago: Year Book Medical, 1986.

Christopher and Dana Reeve Foundation. "Paralysis Resource Center." Christopher and Dana Reeve Foundation, 2013.

Mayo Clinic. "Spinal Cord Injury." Mayo Clinic, October 22, 2011.

MedlinePlus. "Paralysis." MedlinePlus, August 9, 2013.

Rowland, Lewis P., ed. Merritt’s Textbook of Neurology. 12th ed. Philadelphia: Lippincott Williams & Wilkins, 2010.

Smith, Nathalie. "Quadriplegia and Paraplegia." Health Library, March 15, 2013.

Victor, Maurice, and Allan H. Ropper. Adams and Victor’s Principles of Neurology. 9th ed. New York: McGraw-Hill, 2009.

How are Crooks, Curley's wife and Candy lonely and isolated characters?

Almost all of the characters deal with loneliness and isolation to some degree in Steinbeck's novella. The two characters who could be considered the loneliest, however, are Crooks and Curley's wife. For a brief time Candy is also quite lonely.

Crooks is the black stable buck on the ranch. He is also partly crippled after being kicked by a horse. Because he's a black man on a ranch dominated by white men he is the victim of both racism and segregation. He is usually not allowed in the white bunkhouse and the one time he is welcome he is involved in a fight, presumably over race. Candy describes the scene:

"They let the nigger come in that night. Little skinner name of Smitty took after the nigger. Done pretty good, too. The guys wouldn’t let him use his feet, so the nigger got him. If he coulda used his feet, Smitty says he woulda killed the nigger. The guys said on account of the nigger’s got a crooked back, Smitty can’t use his feet.” 

In chapter four Crooks explicitly expresses both the racism he is victimized by and his sense of loneliness and isolation. Crooks explains to Lennie why he's not allowed in the bunkhouse:

“’Cause I’m black. They play cards in there, but I can’t play because I’m black. They say I stink. Well, I tell you, you all of you stink to me.” 

Later while talking to Lennie, Crooks pours his heart out about his sense of loneliness. He tells Lennie how lucky he and George are to have each other to talk to. He says it doesn't even matter what they talk about, it's just the talking that's important. He says,

“A guy goes nuts if he ain’t got nobody. Don’t make no difference who the guy is, long’s he’s with you. I tell ya,” he cried, “I tell ya a guy gets too lonely an’ he gets sick.” 

For a brief time, Crooks's loneliness is assuaged as both Lennie and Candy come into his room. Crooks even offers to lend a hand on the ranch the men are planning on buying. His dream, however, is abruptly put to an end when Curley's wife comes into the barn and begins talking to the men gathered in Crooks's room.

Curley's wife is possibly the loneliest and most isolated character. She is a woman on a ranch full of men. Her husband is often belligerent and treats her poorly. It is even suggested that he cheats on her by going to the whorehouses in Soledad. Thus, she seeks companionship with the other men on the ranch who are generally suspicious of her and use derisive terms such as tramp, tart and floozy to describe her. In both chapter four and five she reveals the level of her loneliness. While talking to Crooks, Lennie and Candy she says,

"Think I don’t like to talk to somebody ever’ once in a while? Think I like to stick in that house alla time?”

As with Crooks, Curley's wife really pours her heart out to Lennie. In chapter five she describes her dreams and how she wound up marrying Curley. She claims she could have been in the movies had it not been for her mother. She even tells Lennie her true feelings about Curley:

"I don’ like Curley. He ain’t a nice fella.” 

Because she feels comfortable with Lennie she allows him to stroke her hair, which, of course, is a terrible idea and it costs her life as Lennie accidentally breaks her neck. Her struggle to seek companionship is fatal. Steinbeck describes her in death:

And the meanness and the plannings and the discontent and the ache for attention were all gone from her face. She was very pretty and simple, and her face was sweet and young. 

Candy is often referred to as being lonely, yet this is only true for a very short time the book. He is old and crippled but at the beginning he has the companionship of his old dog. Unfortunately, the dog is euthanized by Carlson in chapter three. For a brief time Candy feels the misery of loneliness until he hears George talking about the dream of owning his own farm. Candy is immediately interested and offers to put in money to make the dream a reality. The dream ultimately fails and the reader must assume that Candy lived out his days lonely and isolated on the ranch. 

What effect does the opening paragraph have on readers? What is learned about the narrator?

The first paragraph of the story has a lot of information in it, but most of the information has to do with things we infer about the narrator from the way he writes, rather than what he actually says.

There are a few outright facts in the paragraph: we learn that the writer is old. We learn that he has know many law copyists or scriveners. We learn that Bartleby was the oddest one he ever knew.

When we consider how the paragraph is written, however, we can infer quite a bit more. The paragraph is written in a overly formal, legalistic way. The writer is always qualifying his assertions: he means to say that scriveners are fascinating people, but he says only that they "would seem" interesting -- they appear to be interesting, but they might not be interesting at all. Nothing has been written about them -- at least nothing he knows of. He could tell stories that "might" make "good-natured gentlemen" smile. His care in expression, we assume, indicates that he is accustomed to writing like a lawyer.

There are certain assertions, however, that he does not qualify. Bartleby "was the strangest" scrivener he had ever known. No biography of him can be written, because there "no materials exist" on which to base such a work. Even more, he flatly asserts that this "is an irreparable loss to literature." This almost passionate declaration really stands out. There is a hint here that the lawyer really cares for Bartleby, which we find out is indeed the case as we read on.

Of course, the other thing the reader takes away from this paragraph is a certain amount of curiosity about Bartleby, this person about whom so little is known, beyond what the lawyer's "own astonished eyes saw" of him. This lack of information is intriguing. What was so astonishing? Why is the lawyer writing this, if he knows so little about Bartleby?

Finally, we get a sense that maybe, through this writing, legalistic as it may be, the lawyer feels he might somehow be able to connect with Bartleby, or, at least, understand own his own feelings about him. I think that the end result of this paragraph is to show the lawyer as a person who, despite his penchant for legalistic qualification, is still at bottom a feeling individual. And for us readers -- we want to read more.

Why do you think Odysseus wants Polyphemus to know who blinded him?

Odysseus wants Polyphemus to know who blinded him because of his immense pride.  Polyphemus has ignored the religious imperative to offer hospitality to strangers, instead choosing to eat several of Odysseus's crew because he believes himself to be more powerful than the gods.  It is actually Polyphemus's pride that renders him so abhorrent to Odysseus.  As his ship sails away, Odysseus shouts back to shore,

"Cyclops, in the end it was no weak man’s companions you were to eat by violence and force in your hollow cave, and your evil deeds were to catch up with you, and be too strong for you, hard one, who dared to eat your own guests in your own house, so Zeus and the rest of the gods have punished you." (9.475-479)

Odysseus really wants to rub it in that Polyphemus is not as strong as he thinks and that Zeus and the gods have permitted him to wound the Cyclops as punishment for his terrible pride.  But the quality that prompts Odysseus to name himself as "no weak [man]" is his own pride.  And despite the danger the monster still posed to them (via his own strength and because Poseidon is his father), Odysseus continues, "'Cyclops, if any mortal man ever asks you who it was that inflicted upon your eye this shameful blinding, tell him that you were blinded by Odysseus, sacker of cities."  Odysseus very much wants the monster to know the name of the man who bested him.  This can only be the result of his own pride which is so immense that it overcomes any concern for his or his crew's well-being. 

Explain the meaning of "snake-riddle of tank tracks."

It is a pity that you have not provided a reference for this line. It seems suited to either a poem or other literary genre with possibly a military theme. The word 'tank' in this instance is probably a reference to a military tank.

What makes these tracks unique is the fact that they are made by vehicles that use a continuous band for propulsion. The treads are made up of smaller rubber or steel plates which are attached to each other and form a continuous tread driven by two or more wheels. As such, these treads leave a very distinct mark on whatever soft surface they are driven and are, therefore, easily identifiable.

The reference in the above quote is most likely a reference to the marks impressed upon a surface when one or more of these tanks was driven over it. The 'snake riddle' is a metaphor in which the tracks are compared to the marks left behind by a snake as it slithers over a soft surface. Since there are many such tracks, it is difficult to determine where they start and where they end as there is a confusing array of markings, probably crisscrossing each other numerous times, which explains the 'riddle' part of the quote.

I have a question: do you think that knowing about history is important ? Why or why not ? I need the answer as paragraph

As the American philosopher George Santayana wrote, "those who do not remember the past are condemned to repeat it." This quote explains in a nutshell why knowing  history is so important: We need to understand past events and analyze them so that we can try to avoid the mistakes of the past and learn from the successes. This is why, for example, so much energy has been spent on trying to understand the rise of a tyrant like Hitler. Germany in 1933 was a democracy like the United States and was considered one of the most advanced countries in the world, so how did ordinary German people end up electing a genocidal maniac who plunged the world into a highly destructive global war? How can we make sure that doesn't happen again and doesn't happen in our own country? On the positive side, historians spend a good deal of time trying to understand events that went well: how, for example, did the founders of the United States devise a system of governance based on the will of the people (at least free male people) that worked to make the country great when they could so easily have gone in the wrong direction? Ignoring history deprives us of the valuable guidance that such examples from  the past provide. In fact, the ability to record and transmit our history is part of what distinguishes humans from all other animals, who don't have any way that we know of to record or learn from events that happened hundreds or thousands of years ago. Knowing and learning from our history is part of what makes us human. 

Why does Paris want to marry Juliet so soon?

In Act IV, scene i, Paris explains to Friar Laurence his rush to marry Juliet. He says it's because she is grieving too much over her cousin Tybalt's death. She has been spending too much time alone. Juliet's father, Paris says, thinks so much grief is unhealthy, and that a wedding—and a companion to be with—will help her to recover her equilibrium. Love, however, is not the primary motivation at the moment, at least not on Juliet's part, because, as Paris puts it, a person in mourning can't fall in love ("Venus smiles not in a house of tears"). He says,

Immoderately she weeps for Tybalt’s death,

And therefore have I little talked of love,

For Venus [love] smiles not in a house of tears.

Now, sir, her father counts it dangerous

That she do give her sorrow so much sway,

And in his wisdom hastes our marriage

To stop the inundation of her tears—

Of course, Paris has wanted to marry Juliet since the beginning of the play, so this reasoning about haste may well be a rationalization. Paris says to Juliet's father, when he decides on a Monday that Thursday will be the wedding day, that he would just as soon they married even faster.

What ruse does the “Republican” sniper use to shoot the other sniper?

In Liam O'Flaherty's short story, "The Sniper," a soldier is alone on a rooftop in the middle of a street battle during the Irish Civll War. The sniper is a "Republican," meaning he sides with the forces of those who were against the Anglo-Irish treaty. They wanted complete autonomy for Ireland. His opponents were "Free-Staters." They agreed to the treaty which kept Ireland as part of the British Commonwealth.

The Republican sniper is surrounded by his enemies. Simply lighting a cigarette is dangerous as it reveals his position to an opposing Free-State sniper who takes a shot at him. And, after killing a woman and an armored car commander, he is shot in the arm by the enemy sniper. He then devises a way (a "ruse") to get his opponent to reveal himself. He puts his cap over the muzzle of his rifle and raises it above the "parapet" of the roof. When the enemy takes a shot at the cap, the Republican sniper drops the rifle to the street below. Thinking he has killed his enemy, the Free-State sniper stands up on the opposite roof. He is promptly killed by the Republican. The story's surprise ending is quite sad as the sniper discovers the man he has killed was actually his brother. 

How has Jimmy changed in 'A Retrieved Reformation'?

Jimmy's change was triggered by his falling in love at first sight with the beautiful and highly respectable Annabel Adams. It should be noted, however, that he was already beginning to realize that a life of crime is always a mistake. It means that the criminal becomes too well known to law enforcement officers, such as Ben Price. Judges impose harsher sentences. It is easier to get caught and harder to get out. 

He had served nearly ten months of a four year sentence. He had expected to stay only about three months, at the longest.

He also realizes that he is getting to be too well known as the best safecracker in the business. This is brought home to him when the warden seems to know all about him and when his old pal Mike Dolan asks:

“Got anything on?” 

Obviously too many people know about him and too many are talking about him. So Jimmy decides to move all the way to Arkansas, establish a business as a "front," and start operating in a virgin territory. But by chance he sees and falls in love with Annabel Adams. 

Jimmy Valentine looked into her eyes, forgot what he was, and became another man. 

He "became another man," but he was unconsciously preparing to make a radical change before that chance encounter. Annabel is a "catalyst' rather than a "cause" of his reformation. He knows he cannot win her love and remain a criminal. His experience in the shoe shop in prison gives him the idea of opening a shoe shop in Elmore, Arkansas. He is successful because of his sharp mind and winning personality. O. Henry is making the point that a man who has the talent to be a successful criminal can use the same talent to be successful if he goes straight.

In the end, Jimmy's future looks bright. He is a successful and respected citizen, engaged to marry a beautiful girl, accepted by her family and all their friends, on his way to becoming a family man, homeowner, churchgoer, and pillar of the community. He has changed his name to Ralph Spencer in order to put "Jimmy Valentine" well behind him.The change that has taken place in the old Jimmy Valentine is spelled out in the letter he writes a friend to whom he is bequeathing his set of custom-designed and custom-made safecracking tools.

Say, Billy, I've quit the old business—a year ago. I've got a nice store. I'm making an honest living, and I'm going to marry the finest girl on earth two weeks from now. It's the only life, Billy—the straight one. I wouldn't touch a dollar of another man's money now for a million. After I get married I'm going to sell out and go West, where there won't be so much danger of having old scores brought up against me. I tell you, Billy, she's an angel. She believes in me; and I wouldn't do another crooked thing for the whole world. 

For a few tense moments when Ben Price shows up at the bank, it looks as if Jimmy's dreams are  about to be smashed to ruins. But his good deed in saving the life of the little girl accidentally locked in the bank vault, makes such an impression on his nemesis that he is allowed to "retrieve" his reformation and go ahead with his idyllic new life.

How does Stevenson make Dr Jekyll and Mr Hyde's relationship so fascinating?

One major way in which Stevenson makes the relationship between Dr. Jekyll and Mr. Hyde so fascinating is through his use of point of view.  Stevenson employs a third-person limited omniscient perspective; this means that the narrator is not a participant in the story and can report the thoughts and feelings of only one character, and, in this case, that character is Mr. Utterson, Dr. Jekyll's lawyer and friend.  Because we can only learn about events based on what Mr. Utterson sees and hears, the truth about the relationship between Dr. Jekyll and Mr. Hyde remains a mystery to which clues are only revealed bit by bit.  We are put into Utterson's position by being just as in the dark and confused as he is, and so our interest is piqued just as Utterson's is.  Were the story written from Dr. Jekyll's perspective, there would likely be nowhere near as much mystery, and thus we would not find the relationship nearly as fascinating.

In "The Lesson," after her visit to the F.A.O. Schwartz toy store, what does Slyvia realize about her life? How does she plan to make changes?

In Toni Cade Bambara’s story “The Lesson” Sylvia has a thought provoking experience when she visits the F.A.O. Schwartz toy store with Miss Morris and a group of adolescents from her Harlem neighborhood. Sylvia is amazed at the prices of the toys in the store, and even more amazed that people can afford to purchase them. She focuses on a toy clown costing $35. In her mind, she thinks of all the things her family can puchase with that amount of money such as beds for twin boys, or a car trip for the whole family. It dawns on her that there is a double standard when it comes to monetary success. She wonders who can afford to spend that amount of money on a toy, and what they do to make expendable money.

Thirty-five dollars would pay for the rent and the piano bill too. Who are these people that spend that much for performing clowns and $1000 for toy sailboats? What kinda work they do and how they live and how come we ain't in on it? Where we are is who we are, Miss Moore always pointin out.

When the group returns to the neighborhood, Miss Morris engages the children in a conversation about the day. Sylvia’s friend Sugar is vocal about her feelings, which excites Miss Morris and angers Sylvia, who wants to escape to think about the day by herself.

"I think," say Sugar pushing me off her feet like she never done before cause I whip her ass in a minute, "that this is not much of a democracy if you ask me. Equal chance to pursue happiness means an equal crack at the dough, don't it?" Miss Moore is besides herself and I am disgusted with Sugar's treachery.

While Sugar runs ahead to the ice cream store, Sylvia lags behind, vowing to prosper. Sylvia never states exactly what she will do but she does make it clear that she is determined.

We start down the block and she gets ahead which is O.K. by me cause I'm going to the West End and then over to the Drive to think this day through. She can run if she want to and even run faster. But ain't nobody gonna beat me at nuthin.

Was Jean-Jacques Rousseau in favor of collectivism or individualism? How did this influence his political philosophy?

Jean-Jacques Rousseau is generally considered the quintessential collectivist. That is, he believed that the common good of the whole of society must always and everywhere outweigh the rights of individuals to make their own choices.

Rousseau began by arguing that the characteristic feature of human beings that gives us our advantage over other animals is our capacity for cooperation. This is entirely accurate; moreover, it's something I wish more people (including some biologists) better understood. Humans are smarter than other animals, but not that much smarter---our great success is due to our unmatched capacity for cooperation.

However, Rousseau believed that human beings were free and happy before the dawn of civilization, which has largely only brought us misery. This is clearly false; human standard of living has dramatically improved by any measure since the dawn of civilization. Health is the easiest to keep track of, but other measures such as economic prosperity and self-reported happiness also show an upward trend.

Based on his belief that cooperation is the key to the common good, Rousseau argued for a restructuring of society where the government would be democratic but extremely powerful, where almost every aspect of our lives would be shaped by the government forcing us to act toward the common good. He believed in an absolute majority rule by which the state even held the power over life and death by majority vote.

This is not as extreme as it may at first sound, as we do in fact have capital punishment in many democratic countries and military forces in nearly all of them. We do in that sense grant majority vote control over life and death.

Still, I think most people would object to Rousseau's extreme form of collectivism. While I think most people would agree that the common good does matter, and people cannot simply be allowed to do whatever they want even to the point of rape and murder, nonetheless most people believe that individuals deserve to have a certain amount of individual freedom to pursue their own desires and interests without interference from the rest of society. We are in this sense all both collectivists and individualists, or else something in between the two. The question is really where to find the balance---how can we achieve peace and harmony while also preserving personal liberty?

What were the concerns in the North once the slaves were freed?

Concerns surrounding freed slaves varied among Northerners. Many, particularly recent Irish immigrants, worried that freedmen would move to Northern cities and compete with them for jobs. These fears lay behind some Northern opposition to emancipation. After the war was over, political leaders and others in the North debated the meaning of freedom as it related to former slaves in the South. Some Democrats asserted that federal obligations to freedmen extended no further than ending slavery. Other moderates supported some federal action to promote education and to assist former slaves in transitioning to free labor status. So-called "radical" Republicans advocated a robust federal role in securing equality for African-Americans in the South. Their plan included full suffrage for black men, which was established by the Fifteenth Amendment in 1870. It also included the division of the South into military districts, each of which would be charged with providing assistance in securing equality for African-Americans. Only a very few radicals, most of whom had been abolitionists before the war, pushed for land redistribution to benefit the millions of landless slaves. The vast majority of Northerners assumed that blacks would enter into wage labor. These varying concerns about African-American issues contributed to the intense divisions that characterized politics during the Reconstruction era.

What is the relationship between birth defects and drug use?

Drugs as Teratogens

Teratogens (teratogenic substances) are environmental substances that cause birth (or developmental) defects. Thousands of teratogenic substances exist, and a large number of them are drugs, including over-the-counter (OTC) drugs, prescription drugs, and illegal drugs of abuse.

Nearly all teratogens are most detrimental during the embryonic period (the second to eighth week of pregnancy). It is during this period in which organs form. Exposure to teratogenic substances may interfere with this normal organ formation. While drugs that are taken beyond the eighth week of pregnancy are not likely to cause actual birth defects, they may interfere with normal functioning of organs or may interfere with normal growth, causing intrauterine growth retardation. Drugs, like most other teratogens, affect the fetus when they cross the placenta along with oxygen and nutrients. Aspirin is one of the OTC drugs that is teratogenic, potentially causing bleeding in the pregnant woman and the fetus.

The use of prescription drugs may be necessitated because of a medical condition in the pregnant woman. If this is the case, it is essential for the medical professional to prescribe a drug that is not teratogenic or one that is unlikely to harm the fetus. One formerly common prescription drug, the broad-spectrum antibiotic tetracycline, caused discoloration of primary and secondary teeth in utero. Today, another broad-spectrum antibiotic is used to treat infection, decreasing the likelihood of a resultant birth defect.

Generally, when speaking of birth defects and drug use, one more commonly attributes defects to tobacco (smoking), alcohol, marijuana, stimulants, sedatives, addictive substances (like heroin or cocaine), and hallucinogens, most of which are teratogenic. Smoking tends to cause heart defects and intrauterine growth retardation. Alcohol exposure most typically causes fetal alcohol syndrome. This condition generally involves growth retardation and other physical and cognitive problems. No definite evidence exists about the teratogenic effects of marijuana, although the drug has been implicated in cases of small head circumference, neurological problems, and learning deficiencies. Investigations are ongoing into the effects of marijuana on prenatal development, especially because marijuana is the single most common illicit drug used by pregnant women.

Stimulants (including amphetamines) and sedatives (including phenobarbital) seem to cause developmental defects within the nervous system. Cocaine has been found to cause placental abruptions, causing death of pregnant woman and baby, or premature delivery. Opioids like heroin often cause intrauterine growth retardation and cause infants to be born addicted. Also, newborns addicted to heroin or other opioids are likely to have learning disabilities later in life.

Hallucinogens (like LSD or belladonna) differ from the other categories of drugs in that they can cause birth defects even if they are taken years before pregnancy. Hallucinogens have been found to cause chromosomal damage at the time of use. Because chromosomes in egg cells (ova) and in spermatogenic cells may be damaged, a wide variety of birth defects can occur. Similarly, if hallucinogens are used during early pregnancy, chromosomal damage may occur, leading to various types of birth defects. Many pregnant drug-users use more than one type of drug. This complicates the situation in that drugs may interact to have a significantly different and greater effect on the fetus.

Drug Treatment for Pregnant Women

Pregnant women who use heroin or other opioids are often treated with methadone . While this is an effective immediate treatment, it does not prevent a fetus from being born addicted. Suboxone (also known as buprenorphine) is drug used since the 1980s to treat opioid addiction (first used in the United States for this purpose in 2002). According to the National Institute on Drug Abuse, the findings of a 2012 clinical trial suggest that buprenorphine may be a safe and effective alternative to methadone, the standard treatment for opioid dependence during pregnancy. Infants born to mothers on heroin, methadone, or suboxone are evaluated using the neonatal abstinence (Finnegan) scale. The use of this scale determines the course of treatment in stopping the use of these substances.

Bibliography

Boyd, Susan C., and Leonora Marcellus. With Child: Substance Use During Pregnancy—A Woman-Centered Approach. Halifax: Fernwood, 2007. Print.

Huestis, Marilyn A., and Robin E. Choo. “Drug Abuse’s Smallest Victims: In Utero Drug Exposure.” Forensic Science International 128 (2002): 20–30. Print.

Huizink, Anja C., and Eva J. Mulder. “Maternal Smoking, Drinking, or Cannabis Use During Pregnancy and Neurobehavioral and Cognitive Functioning in Human Offspring.” Neuroscience Biobehavioral Review 30 (2006): 24–41. Print.

Rayburn, William, F. “Maternal and Fetal Effects from Substance Use.” Clinical Perinatology 34 (2007): 559–71. Print.

Whitten, Lori. “A Multisite Clinical Trial Lays Groundwork for Improving Care for Mothers and Babies Affected by Opioid Dependence.” Natl. Inst. on Drug Abuse. NIH NIDA, July 2012. Web. 28 Oct. 2015.

What is the name of Hamlet's father?

Though in the printed script Hamlet's father is listed only as "Ghost", we know his actual name from things that are said in the play. Hamlet's father's name is, in fact, also Hamlet. We know this from a few mentions early on. In Act I, Scene 1, Horatio discusses the history of conflict between Denmark and Norway. In that story, he references "Our last king" and goes on to name him "our valiant Hamlet". At the end of the scene, Horatio makes mention of going to see "young Hamlet" (emphasis added), letting us know that the Hamlet so-named in the play is the son of the old King he was talking about before (and whose ghost they just saw). 

The very next scene begins with Claudius also referencing the name of the departed King, saying "Though yet of Hamlet our dear brother's death the memory be green". Again, he's talking about his brother "Old" Hamlet, now dead, and not his nephew "young" Hamlet, who is the title character of the play. Another way to think of it is that the living Hamlet we see in the play is really "Hamlet, Jr". 

In a parallel to Hamlet and Hamlet (and to make things even more confusing for modern readers), the Norwegian King and prince mentioned in the play are both named Fortinbras. Old Hamlet killed Old Fortinbras years before the play begins. But with the start of the play, Old Hamlet is dead and Young Fortinbras (or Fortinbras, Jr.) sets out with an army to claim some disputed land, which is witnessed and commented on by Young Hamlet. 

New York City has been both at the forefront of America’s great diversity and at the forefront of America’s historical nativism. Explain.

New York City has been at the forefront of American diversity for a long time because of the fact that it is the most important city in the US both economically and culturally.  It has been at the forefront of nativism because it has been at the forefront of diversity.

People from other countries tend to come to the United States in search of economic opportunity.  The greatest economic opportunity, particularly in times past, existed in cities.  As America’s leading economic powerhouse, New York was a city full of factories and other workplaces where immigrants could find jobs.  For this reason, immigrants came to New York City in large numbers.  Because New York is and was America’s foremost city, internal migrants moved there as well. African Americans came up from the South in the Great Migration.  People of all races from all parts of the country move there because they are attracted to its glamor and its opportunities.  All of this has helped to make New York the center of America’s great diversity.

Because New York has been the center of so much diversity, it has also been a center of nativism.  This is not strange.  It would be surprising if nativism were to arise only in places with very few immigrants.  Instead, it makes sense that at least some of the people most strongly affected by immigration and diversity would take part in a backlash against it.  Since the “native American” people of New York City have been so strongly affected by immigration over the years, they have often been part of the reaction to (and against) immigrants and diversity.

What kind of man would Westley grow up to be based on Langston Hughes's description of him in his autobiographical short story "Salvation"?

In his autobiographical short short "Salvation," Langston Hughes relays that, as the congregation continued to pray for the salvation of the children on the mourner's bench, more and more children came forward to be saved until just he and a boy named Westley were the last two children remaining on the bench. After more praying and crying and singing, Westley whispered to Langston, "God damn! I'm tired o' sitting here. Let's get up and be saved."

Once Langston was the last child remaining on the bench, he further reflects watching Westley on the platform, "swinging his knickerbockered legs and grinning down at me" and noting that "God had not struck Westley dead for taking his name in vain or for lying in the temple." If we were to draw conclusions about what kind of man Westley grew up to be, we could certainly reach one of two conclusions.

On the one hand, Westley's actions showed disbelief, disrespect, and the ability to manipulate a situation to his own advantage, all characteristics that point to Westley growing up to be a man with few morals and poor character, the sort of man who easily winds up on the path towards jail.

Yet, on the other hand, Hughes's short story leaves open to interpretation exactly what the moment of salvation truly is. Due to the amount of figurative language, such as the use of hyperbole, in his aunt's explanation of what the moment of salvation is like, we know that the adult Langston no longer takes his aunt's explanation seriously. So, the story leaves unanswered the question, what exactly is the moment of salvation? It further begs the question, were Westley and Langston truly lying when they "got up and [were] saved"? The whole point of the preacher's story of the lost lamb is that the lamb was just that--lost. As a lost lamb, it was not a perfect lamb, just as Westley was not a perfect lamb. No one in a state of perfection can reach salvation because there is nothing to be saved. Since Westley displayed the characteristics of one who is most lost, one can presume that he was actually truly saved, maybe more saved than the rest of them. Therefore, one can also presume that Westley grew up to change his life around.

What is the gastrointestinal system?

Structure and Functions

The gastrointestinal system or alimentary canal exists as a tube that runs through the body from mouth to anus. The wall of the tube is composed of four layers of tissue. The outermost layer, the serosa, is part of a large tissue called the peritoneum, which covers internal organs and lines body cavities. Extensions of the peritoneum called mesenteries anchor the organs of digestion to the body wall. Fatty, apronlike structures that hang in front of the abdominal organs are also modifications of the peritoneum. They are called the lesser and the greater omentum. The muscular layer, composed of circular and longitudinal muscles, makes up the bulk of the wall of the tube. The contractions of this layer aid in moving materials through the tube. Nerves, blood vessels, and lymph vessels are found in the third layer, the submucosa. The innermost or mucous layer has glands for secretion and modifications for absorption.

The tube is compartmentalized, and each section is equipped to accomplish some part of the digestive process. The mechanical phase of digestion involves the physical reduction of food to a semiliquid state; this is accomplished by tearing, chewing, and churning the food. Chemical digestion utilizes enzymes to reduce food to simple molecules that can be absorbed and used by the body to provide energy and to build and repair tissue.

The mouth (also called the buccal or oral cavity) marks the beginning of the gastrointestinal system and the digestive process. The mouth is divided into two areas. The vestibule is the space between the lips, cheeks, gums, and teeth. Lips, or labia, are the fleshy folds that surround the opening to the mouth. The skin covers the outside, while the inside is lined with mucous membrane. The colored part of the lips, called the vermilion, is a juncture of these two tissues. Because the tissue at this point is unclouded, underlying blood vessels can be seen. A membrane called the labial frenulum attaches each lip to the gum, or gingivalum.

The oral cavity occupies the space posterior to the teeth and anterior to the fauces or opening to the throat. It is bounded on the sides by cheeks and on the roof by an anterior bony structure called the hard palate and a posterior muscular area, the soft palate. The uvula, a cone-shaped extension of the soft palate, can be seen hanging down in front of the fauces. The floor of the oral cavity is formed by the tongue and associated muscles. Taste buds are found on the surface of the tongue. The bottom of the tongue is anchored posteriorly to the hyoid bone. Anteriorly, the membranous frenulum lingua anchors the tongue to the floor of the mouth. The tongue’s movement is controlled by extrinsic muscles that form the floor of the mouth and by intrinsic muscles that are part of the tongue itself. The movements of the tongue assist in speaking, swallowing, and forming food into a bolus.

Teeth, found in gum sockets, are the principal means of mechanical digestion in the mouth. Human teeth appear in two sets. The deciduous or milk teeth are the first to appear. There are usually ten in each jaw, and they are replaced by the second, permanent set during childhood. The permanent set consists of sixteen teeth in each jaw. The four incisors and two canines have sharp chiseled edges, which permit biting and tearing of food. The four premolars and six molars have flat surfaces that are used in grinding the food. Frequently, the third pair of molars or wisdom teeth do not erupt until later in adolescence. The crown of a tooth appears above the gum line while the roots are embedded in the gum socket. The small area between the crown and the root is called the neck. The crown is covered with enamel and the root with cementum. Dentin is beneath the covering in both areas and forms the bulk of the tooth. The central cavity of the tooth is filled with a soft membrane called pulp. Blood vessels and nerves are
embedded in the pulp.

At the rear of the mouth, the fauces or opening leads to the pharynx. The pharynx is a common passageway for the movement of air from nasal cavity to trachea and food from mouth to esophagus. The esophagus is a tube approximately twenty-five centimeters long. Most of the esophagus is located within the thoracic cavity, although the lower end of the tube pierces the diaphragm and connects with the stomach in the abdominal cavity. Both ends of the esophagus are controlled by a circular muscle called a sphincter. The movement of food through the esophagus is assisted by gravity and the contractions of the muscularis layer. No digestion is accomplished in either the pharynx or the esophagus.

The stomach, a J-shaped organ, is divided into four areas: the cardia, fundus, body, and pyloris. The cardia lies just below the sphincter at the juncture of esophagus and stomach, while the fundus is a pouch that pushes upward and to the left of the cardia. The large central area is the body, and the lower end of the stomach is the pyloris. Here another sphincter, the pyloric valve, controls the opening between stomach and intestine. The mucosa of the stomach is arranged in folds called rugae. The rugae permit distension of the organ as it fills. Gastric and mucus glands are present in the mucosa. The gastric glands produce and secrete enzymes that are specific for protein digestion, as well as hydrochloric acid, which creates the proper acid environment for enzyme action. The muscularis of the stomach wall has three layers of muscle with a circular, longitudinal, and oblique arrangement. The muscle arrangement facilitates the churning action that reduces the food to a semiliquid called
chyme. The pyloric valve relaxes under neuronal and hormonal influence, and the chyme is moved into the small intestine.

The site for the completion of digestion and the absorption of digested material is the small intestine. This tube, with a 2.5-centimeter diameter and a length of 6.4 meters, is coiled into the mid and lower abdomen. The first twenty-five centimeters of the small intestine constitute the duodenum. This is followed by the jejunum, which is 2.5 meters long. The ileum, at 3.6 meters, terminates at the ileocecal valve, which connects the small to the large intestine. The interior of the small intestine is characterized by the presence of fingerlike projections of the mucosa called villi that contain blood and lymph capillaries and circular folds of submucosa (the plicae circularis), both of which provide absorption surface for the digested food. Mucosal glands produce enzymes that contribute to the digestion of carbohydrates, lipids, and proteins. Enzymes from the pancreas and bile from the liver enter the small intestine at the duodenum and aid the chemical digestion.

The final compartment in the gastrointestinal system is the large intestine, sometimes called the bowel or colon. This tube, with a diameter of 6.5 centimeters and a length of 1.5 meters, is divided into the cecum; the ascending, transverse, and descending colon; the rectum; and the anal canal. The cecum is a blind pouch located just below the ileocecal valve. The fingerlike appendix is attached to the cecum. The ascending colon extends from the cecum up the right side of the abdomen to the underside of the liver, where it turns and runs across the body. The colon descends along the left side of the abdomen. The last few centimeters of colon form an S-shaped curve that gives the section its name, sigmoid colon. Three bands of longitudinal muscle called taeniae coli run the length of the colon. Contraction of these bands causes pouches or haustra to form in the colon, giving the tube a puckered appearance. The sigmoid colon leads into the rectum, a twenty-centimeter segment that terminates in a short anal canal. The anus is the opening from the anal canal to the exterior of the body.

Disorders and Diseases

Because the primary function performed in the gastrointestinal system is the physical and chemical preparation of food for cellular absorption and use, any malfunction of the process has implications for the overall metabolism of the body. Structural changes or abnormalities in the anatomy of the system interfere with the proper mechanical and chemical preparation of the food.

Teeth are the principal agents of mechanical digestion or mastication in the mouth. Dental caries or tooth decay involves a demineralization of the enamel through bacterial action. Disrupted enamel provides an entrance for bacteria to underlying tissues, resulting in infection and inflammation of the tissues. The resulting pain and discomfort interfere with the biting, chewing, and grinding of food. Three pairs of salivary glands secrete the water-based, enzyme-containing fluid called saliva. These glands can be the target of the virus that causes mumps. (Although the pain and swelling that are typical of this disease can prevent swallowing, the more important effect of the virus in males is the possible inflammation of the testes and subsequent sterility.)

The gastroesophageal sphincter at the lower end of the esophagus controls the movement of materials from the stomach into the esophagus. Relaxation of this sphincter allows a backflow of food (gastroesophageal reflux

) to occur. The acidity of the stomach contents damages the esophageal lining, and a burning sensation is experienced. Substances such as citric fruits, chocolate, tomatoes, alcohol, and nicotine as well as body positions that increase abdominal pressure, such as bending or lying on the side, induce heartburn or indigestion. A hiatal hernia
occurs when a defect of the diaphragm allows the lower portion of the esophagus and the upper portion of the stomach to enter the chest cavity; it causes
heartburn and difficulty in swallowing.

Pathologies and abnormalities of the stomach and intestines are studied in the medical science called gastroenterology. The stomach is the site of both mechanical and chemical digestion. Although small amounts of digested food begin to pass into the small intestine within minutes following a meal, the chyme usually remains in the stomach for three to five hours. Relaxation of the gastroesophageal sphincter will result in reflux; and stimulation by nerves from the medulla of the brain can cause the forceful emptying of stomach contents through the mouth. This is called vomiting and may be brought about by irritation, overdistension, certain foods, or drugs. Excessive vomiting results in dehydration, which in turn upsets electrolyte and fluid balance.

Chemical digestion in the stomach requires an acidic environment. This is provided by gastric glands, which secrete hydrochloric acid. The tissue lining the stomach protects it from this acidity and prevents self-digestion. Oversecretion of the gastric juices or a breakdown of the stomach lining can cause lesions or peptic ulcers to form in the mucosal lining. Gastritis, the inflammation of the stomach mucosa brought on by the ingestion of irritants such as alcohol and aspirin or an overactive nervous stimulation of the gastric glands, may be the underlying cause of ulcer formation. Ulcers can form in the lower esophagus, stomach, and duodenum because these are the organs that come in contact with gastric juice. The terms “gastric ulcer” and “duodenal ulcer” refer to peptic ulcers located in the stomach and the first portion of the small intestine, respectively.

Gastroenteritis could involve the stomach, the small intestine, or the large intestine. It is a disorder marked by nausea, vomiting, abdominal discomfort, and diarrhea. The condition has various causes and is known by several names. Bacteria are a common cause of the condition known as food poisoning
. Amoebas, parasites, and viruses can bring about the symptoms associated with intestinal influenza or travelers’ diarrhea. Allergic reactions to food or drugs may cause gastroenteritis.

Although diverticulitis may be found anywhere along the gastrointestinal tract, it is most commonly found in the sigmoid colon. This disorder results from the formation of pouches or diverticula in the wall of the tract. Undigested food and bacteria collect in the diverticula and react to form a hard mass. The mass interferes with the blood supply to the area and ultimately irritates and inflames surrounding tissue. Abscess, obstruction, and hemorrhage may develop. A diet lacking in fiber appears to be the major contributor to this disorder.

Colitis, or inflammation of the bowel, is accompanied by abdominal cramps, diarrhea, and constipation. It may be brought about by psychological stress, as in irritable bowel syndrome, or may be a manifestation of such disorders as chronic ulcerative colitis and Crohn’s disease.

A change in the rate of motility through the colon or large intestine results in one of two disorders: diarrhea or constipation. As food passes through the colon, water is reabsorbed by the body. If the food moves too quickly through the colon, then much of the water will remain in the feces and diarrhea results. Severe diarrhea affects electrolyte balance. Viral, bacterial, and parasitic organisms may initiate the rapid motility of substances through the colon. Another condition, called constipation, develops from sluggish motility. When the food remains for too long a time in the bowel, too much water is reabsorbed by the body. The feces then become dry and hard, and defecation is difficult. Lack of fiber in the diet and lack of exercise are the leading causes of constipation.

Hemorrhoids are varicose veins that develop in the rectum or anal canal. Varicose veins are the result of weakened venous valves. Factors such as pressure, lack of muscle tone as a result of aging, straining at defecation, pregnancy, and obesity are among the common contributors. Hemorrhoids become irritated and bleed when hard stools are passed.

Malignancies can occur at any point along the gastrointestinal tract. Cancers of the mouth are frequently associated with tobacco use. Esophageal cancer may be associated with heavy alcohol use, tobacco, or chronic reflux. Gastric cancer may be the result of chronic ulcer disease or heavy exposure to foods high in nitrites. Colon cancer is one of the leading causes of death in the United States, and it may be associated with certain genetic disorders or might arise spontaneously.

Disorders in the accessory organs contribute to the malfunctioning of the gastrointestinal system. Gallstones, cirrhosis of the liver, pancreatitis, and pancreatic cancer are among the major diseases affecting the digestive process. These disorders generally involve the obstruction of tubes or the destruction of glands, so that enzymes do not reach the intended site of digestion.

Perspective and Prospects

The proper functioning of the gastrointestinal system is dependent on the anatomical structure and health of the organs. The organs provide the site for the mechanical and chemical digestion of food, the absorption of food and water, and the elimination of waste material. Two factors play a primary role in causing anatomical abnormalities in digestion: aging and eating disorders.

The aging process gradually changes anatomical structure. For food to be chewed properly, teeth must be in good health. Dental caries, periodontal disease, and missing teeth prevent the proper mastication of food. Because of these problems, older people tend to avoid foods that require chewing. This may lead to an unbalanced diet. Another age-related change in the mouth is the atrophy of the salivary glands and other secretory glands, which interferes with chemical digestion and swallowing. A loss of muscle tone in the organ walls impedes mechanical digestion and slows down the movement of food through the system. Often, the elimination of waste material becomes difficult and constipation results.

Eating disorders such as anorexia nervosa and bulimia contribute to digestive malfunctioning. These disorders are most often associated with but are not limited to young women. Anorexia is self-imposed starvation, while bulimia is characterized by a binge-purge cycle that incorporates vomiting and/or abuse of laxatives. Both conditions induce nutrient deficiencies and upset water and electrolyte balances. The vomiting of the acid contents of the stomach damages esophageal, pharyngeal, and mouth tissue. It also destroys tooth enamel. In addition to the harm done to the gastrointestinal system, eating disorders affect several other systems, such as the reproductive system.

The field of medical science that studies and diagnoses digestive system disorders is gastroenterology. Gastroenterologists use several investigative techniques. Blood tests and stool examination are used to detect internal bleeding and deficiency disorders. For a time, X rays were the only nonsurgical means of obtaining information on the structure of internal organs. The advent of nuclear medicine
in the 1950s led to the use of radioisotopes in body scanning procedures. Instruments capable of a more detailed and direct visualization were developed, such as fiber optics and the fluoroscope. Fiber optics
involves the use of long, threadlike fibers of glass or plastic that transmit light into the organ and reflect the image back to the viewer; this method allows the physician to detect ulcers, lesions, neoplasms, and structural abnormalities. The fluoroscope uses X rays to permit continuous observation of motion within the organs.

The 1970s saw the development of more sophisticated scanning and imaging techniques. computed tomography (CT) scanning uses X-ray techniques to scan very thin slices of tissue and presents a defined, unobstructed view. Magnetic resonance imaging (MRI) can provide detailed information even to the molecular level; energies from powerful magnetic fields are translated into a visual representation of the structure being studied. Another technique, ultrasonography, passes sound waves through a body area, intercepts the echoes that are produced, and translates them into electrical impulses, which are recorded and interpreted by the physician.

Bibliography

Abrahams, Peter H., Sandy C. Marks, Jr., and Ralph Hutchings. McMinn’s Color Atlas of Human Anatomy. 6th ed. St. Louis, Mo.: Mosby/Elsevier, 2008.

Carson-DeWitt, Rosalyn. "Ulceratuve Colitis." Health Library, September 10, 2012.

Keshav, Satish, and Adam Bailey. The Gastrointestinal System at a Glance. Malden, Mass.: Blackwell, 2013.

Moog, Florence. “The Lining of the Small Intestine.” Scientific American 245 (November, 1981): 154–176.

Shannon, Diane W. "Viral Gastroenteritis." Health Library, September 26, 2012.

Tortora, Gerard J., and Bryan Derrickson. Principles of Anatomy and Physiology. 12th ed. Hoboken, N.J.: John Wiley & Sons, 2009.

Young, Emma. "Alimentary Thinking." New Scientist 2895 (December 15, 2012): 38–42.