Types of Disease (Magill’s Medical Guide, Sixth Edition)
It is difficult to answer the question “What is disease?” To the patient, disease means discomfort and disharmony with the environment. To the treating physician or surgeon, it means a set of signs and symptoms. To the pathologist, it means one or more structural changes in body tissues, called lesions, which may be viewed with or without the aid of magnifying lenses.
The study of lesions, which are the essential expression of disease, forms part of the modern science of pathology. Pathology had its beginnings in the morgue and the autopsy room, where investigations into the cause of death led to the appreciation of “morbid anatomy”—at first by gross (naked-eye) examination and later microscopically. Much later, the investigation of disease moved from the cold autopsy room to the patient’s bedside, from the dead body to the living body, on which laboratory tests and biopsies are performed for the purpose of establishing a diagnosis and addressing proper treatment.
Diagnosis is the art of determining not only the character of the lesion but also its etiology, or cause. Because so much of this diagnostic work is done in laboratories, the term “laboratory medicine” has gained in popularity. The explosion in high technology has expanded the field of laboratory medicine tremendously. The diagnostic laboratory today is highly automated and sophisticated, containing a team of laboratory technologists and...
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Causes of Disease (Magill’s Medical Guide, Sixth Edition)
By far the most common cause of disease is infection, especially by bacteria. Certain lowly forms of animal life known as animal parasites may also live in the body and produce disease; parasitic diseases are common in poor societies and countries. Finally, there are viruses, forms of living matter so minute that they cannot be seen with the most powerful light microscope; they are visible, however, with the electron microscope. Viruses, as agents of disease, have attracted much attention for their role in many diseases, including cancer.
Bacteria, or germs, can be divided into three morphologic groups: cocci, which are round; bacilli, which are rod-shaped; and spirilla or spirochetes, which are spiral-shaped, like a corkscrew. Bacteria produce disease either by their presence in tissues or by their production of toxins (poisons). They cause inflammation and either act on surrounding tissues, as in an abscess, or are carried by the bloodstream to other distant organs. Strep throat is an example of a local infection by cocci—in this case, streptococci. Some dysenteries and travelers’ diarrheas are caused by coliform bacilli. Syphilis is an example of a disease caused by a spirochete. The great epidemics of history, such as bubonic plague and cholera, have been caused by bacteria, as are tuberculosis, leprosy, typhoid, gas gangrene, and many others. Bacterial infections are treatable with antibiotics, such as...
(The entire section is 1050 words.)
Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
It is sometimes said that the nature of disease is changing, that one hears more often of people dying of heart failure and cancer than was once the case. This does not mean that these diseases have actually become more common, although more people do die from them. This increase is attributable to a longer life span and vastly improved diagnostic methods.
For primitive humans, there were no diseases, only patients stricken by evil; therefore, magic was the plausible recourse. Magic entails recognition of the principle of causality—that, given the same predisposing conditions, the same results will follow. In a profound sense, magic is early science. In ancient Egypt, the priests assumed the role of healers. Unlike magic, religion springs from a different source. Here the system is based on the achievement of results against, or in spite of, a regular sequence of events. Religion heals with miracles and antinaturals that require the violation of causality. The purely religious concept of disease, as an expression of the wrath of gods, became embodied in many religious traditions.
The ancient Greeks are credited with attempts at introducing reason to the study of disease by asking questions about the nature of things and considering the notion of health as a harmony, as the adjustment of such opposites as high and low, hot and cold, dry and moist. Disease, therefore, was a disharmony of the four elements...
(The entire section is 395 words.)
For Further Information: (Magill’s Medical Guide, Sixth Edition)
Biddle, Wayne. A Field Guide to Germs. 2d ed. New York: Anchor Books, 2002. This comprehensive book is easily accessible to the nonspecialist and includes a discussion of nearly every virus, bacterium, and fungus known to cause human and nonhuman animal disease. The history of the microbe and the treatment of diseases are included.
Boyd, William. Boyd’s Introduction to the Study of Disease. 11th ed. Philadelphia: Lea & Febiger, 1992. A textbook for students in the medical and allied health sciences. The text and illustrations emphasize the view of disease as a disturbed functional alteration.
Frank, Steven A. Immunology and Evolution of Infectious Disease. Princeton, N.J.: Princeton University Press, 2002. Blends research from molecular biology, immunology, pathogen biology, and population dynamics to discuss how and why parasites vary to escape recognition by the immune system, vaccine design, and the control of epidemics.
Grist, Norman R., et al. Diseases of Infection: An Illustrated Textbook. 2d ed. New York: Oxford University Press, 1992. An informative survey of communicable diseases. Contains copious illustrations.
Kumar, Vinay, Abul K. Abbas, and Nelson Fausto, eds. Robbins and Cotran Pathologic Basis of Disease. 8th ed. Philadelphia: Saunders/Elsevier, 2010. The standard textbook on disease for medical students.
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Disease (Encyclopedia of Science)
Disease can be defined as any change in body processes that impairs its normal ability to function. The human body has certain basic requirements that must be met if it is to function normally. These requirements include the proper amount of oxygen, acidity, salinity, and other conditions. These conditions must all be maintained within a very narrow range. A deviation from that range can cause disease to develop.
Most diseases can be classified into one of three major categories: infectious diseases; noninfectious diseases; and diseases for which no cause has yet been identified. At one time, a number of conditions were also classified as genetic diseases. This category includes conditions such as sickle-cell anemia, phenylketonuria, Tay-Sachs disease, cystic fibrosis, and galactosemia. These conditions are now more appropriately known as genetic disorders.
At one time, humans were totally mystified as to the causes of common diseases such as typhoid, typhus, pneumonia, mumps, yellow fever, pneumonia, smallpox, rabies, syphilis, gonorrhea, tuberculosis, and rheumatic fever. Explanations ranged from punishment by God for evil deeds to acts of magicians or witches to an unbalance in the composition of the blood.
During the eighteenth century, the true nature of such diseases was finally discovered....
(The entire section is 1894 words.)