Poliomyelitis

Poliomyelitis, infectious viral disease that sometimes results in paralysis. The infection chiefly affects children and young adults and is caused by any one of three related viruses called polioviruses.

Doctors diagnose polio by isolating the virus from an infected person using throat cultures, stool samples, or samples of fluids from the brain and spinal cord. Blood tests that indicate the presence of antibodies specific for the virus will also confirm a poliovirus infection.

As yet there is no cure for polio—no drug or other medical treatment can halt the destruction of poliovirus in the body. However, several medical treatments can lessen the severity of the disease. Mild cases of polio do not require specific treatment. For the more serious cases of paralytic polio, keeping patients still and quiet can, in some cases, minimize the severity of paralysis. For these patients initial treatment consists of immediate hospitalization and strict bed rest. Simple treatments, including moist heat applied to affected muscles, can ease pain. Antispasmodic drugs can help patients who suffer involuntary muscle contractions as a consequence of nerve damage.

Vaccines work by exposing the body’s immune system to a microbial infection that is strong enough to provoke an immune response but not severe enough to result in full-blown illness. Once the body has overcome the vaccine-induced challenge of a given infection, the resulting antibodies can recognize and quickly handle any subsequent invasion by the same agent.

Psychosis

Psychosis, mental illness in which a person loses contact with reality and has difficulty functioning in daily life. Psychotic symptoms can indicate severe mental illnesses, such as schizophrenia and bipolar disorder. Unlike people with less severe psychological problems, psychotic individuals do not usually recognize that their mental functioning is disturbed.

Peritonitis

Peritonitis, inflammation of the membrane that lines the abdominal cavity and the organs contained therein. Peritonitis is most often an acute illness, caused by introduction of infection from a perforation of the bowel such as a ruptured appendix or diverticulum. The disease is also caused by introduction of chemically irritating material such as stomach acid from a perforated ulcer or bile from a rupture of the gall bladder or laceration of the liver. Localized peritonitis most often occurs in the pelvis from an infected fallopian tube or a ruptured ovarian cyst. Occasionally peritonitis may occur when the rupture of an abscess causes pus to spill into the abdominal cavity. This sometimes follows surgery inside the bowel with leaking from the site of closure, or from a stab wound through the abdominal wall. Occasionally peritonitis may occur from inflammation of the peritoneal membrane such as in kidney failure, rheumatic fever, and lupus erythematosus. The principal symptom is severe abdominal pain much aggravated by any motion. The patient often has nausea and vomiting and usually is feverish. Untreated cases of acute peritonitis are often fatal. Treatment is directed at the underlying cause. In addition, intravenous fluids and antibiotics are given.

Pus

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Pus, thick white or yellowish fluid, found at sites of bacterial infection of the body. Certain white blood cells, called phagocytes, migrate to the area of infection and engulf the invaders. They then kill the ingested bacteria by releasing toxic substances inside the cell. In the process the white blood cells also die, and these cells become constituents of pus. See Abscess; Carbuncle.

Yogurt, Cheese, and Other Fermented Milk Products

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Fermented milk products, including yogurt and cheese, are formed when bacteria break down lactose to produce lactic acid, which sours the milk. Yogurt is usually made from milk that has been fortified by the addition of nonfat powdered milk to improve its texture and taste. The fortified milk is pasteurized at a very high temperature and homogenized. A culture containing the bacteria Streptococcus thermophilus and Lactobacillus bulgaricus, and sometimes Lactobacillus acidophilus, is then added. The two most popular types of yogurt sold are Swiss-style, with added fruit mixed throughout, and sundae-style, with fruit on the top or bottom.

Cultured buttermilk and sour cream, like yogurt, are produced by the breakdown of lactose by bacteria. Cultured buttermilk used to be made from buttermilk, but is now more commonly made from skim milk. Sour cream is made from cream. Both have a tangy, sour taste imparted by lactic acid.

Cheese making is a complex process, with each of the more than 400 varieties of cheeses differing in the details of the process. However, most cheese making follows the same basic steps. Bacteria are introduced into milk that consume lactose and produce lactic acid. Cheeses are allowed to ferment longer than yogurt, buttermilk, and sour cream, which gives the bacteria time to also digest some of the fat and protein present. The waste products produced by bacteria from digesting fats and proteins provide cheeses with their distinctive and stronger flavors. Acidification of milk or the addition of the enzyme rennin precipitates moist lumps of protein called curds. The curds contain all of the milk’s protein and most of the fat, minerals, and vitamins. The residual thin liquid is known as whey. The curds are salted (for taste) and pressed into shape, which eliminates more of the whey. The pressed curd is then cured under controlled temperature and humidity for varying lengths of time to produce cheese.

Cream, Butter, and Ice Cream

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In order for a product to be labeled as cream, it must contain 18 percent milk fat or more. Light whipping cream must contain at least 30 percent fat, and 36 percent fat is the minimum fat content for heavy whipping cream. Half-and-half, an equal mixture of both milk and cream, must have at least 10.5 percent fat. The various grades of cream are valued for their smooth, thick texture. They are often used in cooking instead of milk, because they are less likely to form a skin when heated and can be whipped into a stiff foam.

When chilled cream is churned gently, the fat globules gather together to form butter, leaving buttermilk as the by-product. Butter contains at least 82.5 percent fat. In the past, before the advent of widespread refrigeration, salt was added to butter to retard bacterial spoilage; now salt is added mainly for flavor.

Ice cream, a popular frozen dessert, is made of milk, cream, sugar, and flavoring. The mixture is slowly beaten while chilled until it is partially frozen, then packed into containers, and chilled until firm. Variants of ice cream include ice milk, which contains less fat; sherbet, which has even less fat; and French ice cream, which is enriched with egg yolks.

Milk Products

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Milk in its natural form, directly from a cow, is called raw milk. It is an extremely versatile product from which a myriad of commercial products are derived.

A. Whole Milk, Low-fat Milk, and Skim Milk

Since the fat in raw milk is lighter in weight than the rest of the milk, it will naturally rise to form a layer of cream if allowed to stand. Spinning the milk in a large machine, called a centrifuge, accelerates the formation of a cream layer, or the separation of fat, from raw milk. Varying amounts of fat are removed from the raw milk, resulting in different kinds of fresh milk. If the fat content is lowered to 3.25 percent, the milk is sold as whole milk. Low-fat milk typically has 1 percent or 2 percent fat. Skim milk, or nonfat milk, is the liquid that remains after removing all the cream; it contains about half a percent milk fat. About half of the milk produced in the United States is consumed as one of these types of fresh milk; the rest is processed into other products such as cream, butter, cheese, yogurt, and ice cream.

Once the fat level has been reduced to the desired level, most fresh milk is homogenized to prevent the further separation of a cream layer. Homogenization is accomplished by forcing hot milk under high pressure through small nozzles. The fat globules become so small that they remain evenly dispersed throughout the milk. In order to insure its safety for human use, almost all milk undergoes pasteurization, in which milk is heated to a high temperature for a specified length of time to destroy pathogenic bacteria. Pasteurized milk can be stored in a refrigerator for a week or longer. Ultrapasteurized milk, common in Europe and Canada, is heated to an even higher temperature and can be stored at room temperature for several weeks.

Condensed, evaporated, and powdered milk are produced by evaporating some or all of the water in milk. Sweetened condensed milk is sweetened with the addition of sugar. These products have very long shelf lives.

B. Cream, Butter, and Ice Cream

C. Yogurt, Cheese, and Other Fermented Milk Products