Medicine is among the most ancient of human occupations. Evidences of the practice of ritual healing, combining religion and primitive science, are found in the earliest traces of communal living. Until the period of the Enlightenment, medical science and technology advanced at a relatively slow and steady rate in the world's major cultures. With the birth of modern science and the onset of the Industrial Revolution, the progress of medicine also began to accelerate. In spite of the breathtaking rapidity of developments in modern medicine, however, it is all of a piece. Hippocrates would quickly have appreciated that contemporary medical practices are founded on principles similar to medicine in his own day. PRIMITIVE MEDICINE Wherever humans have formed social groups, some individuals have taken the role of the healer, responsible for preventing disease and curing the sick. Magic and the use of charms, spells, and incantations frequently were employed. Signatures--such as lion's heart, to be eaten for courage, or plants with leaves resembling body organs, to be used to cure disorders of that organ--were used worldwide. Throughout the ages, \Lshaman\ls and medicine men have discovered valuable information that then was handed down from generation to generation. If possible, the information was kept within the priesthood. Much essential health information escaped, however, to become part of common lore. Therapies for illnesses were more easily kept within the bounds of the priesthood. As recently as the 18th century, William WITHERING, a British physician, obtained information about \Tdigitalis\t, a compound obtained from the foxglove plant and one of the most important drugs used today, from an English witch. Morphine, quinine, ephedrine, and rauwolfia, all used today, come from ancient, prescientific lore. Primitive medicine men learned to set fractures; they even performed such complex procedures as trephination--boring holes in the skull to treat disease. Throughout recorded history, the rational and the magical approaches have existed side by side. EGYPTIAN MEDICINE What is known of Egyptian medicine comes principally from two large fragments of writing, the Ebers papyrus and the Smith papyrus. These papyruses were written about 1600 BC; the Ebers text is a compilation from many sources, and the Smith is probably a copy of a text written about 2500 BC. The Ebers papyrus includes incantations for specific illnesses as well as invocations to the gods; careful case histories and valuable prescriptions, such as castor oil as a cathartic and tannic acid for burns, also were recorded. The Smith papyrus, on the other hand, includes surgical advice that remains pertinent today, such as the use of compression to stop bleeding, and sections on diseases of the eye and the heart and other internal organs. The practices outlined resemble those of modern medicine--defining the disease, stating its symptoms, indicating what the physician should find upon examination, suggesting therapy, and giving a prognosis. The greatest Egyptian physician was Imhotep (about 2800 BC), who also was the architect of the Step Pyramid of Saqqarah. MIDDLE EASTERN MEDICINE About 2000 BC the Amorites unified the nations and tribes in the valleys of the Tigris and Euphrates rivers. They built Babylon, and science and learning flourished under their greatest king, Hammurabi. The Code of Hammurabi, which constitutes wide-ranging laws inscribed on a great stone pillar, includes definitions of the conduct of a physician--what he may treat, what his fee should be--and also prescribes punishments for malpractice. The Hebrew civilization developing at about the same time placed strong emphasis on public health and sanitation. It codified these practices in the Pentateuch and Talmud as prescribed by Moses. The practice of medicine in ancient Israel was one of the duties of the priesthood. ORIENTAL MEDICINE The healing arts in the Orient have had a long and complex history. In several of the major Oriental cultures, forms of medicine involved elaborate theories encoded in multivolume series of texts. Such systems are now referred to as traditional medicine (see \Tmedicine, traditional\t). India Throughout much of their history, the Indians came into contact with the Persians, Greeks, and Chinese, with whom they exchanged information. About 900 BC the Ayurveda, written in India, combined descriptions of disease with information on herbs and magic. The first great Hindu physician known, Charaka, practiced about 1000 BC. Susruta, in the 5th century AD, noted the relationship of malaria to mosquitoes and of plague to rats, knew of more than 700 medicinal plants, and described more than 100 surgical instruments. He treated fractures, removed tumors and kidney stones, and delivered babies by Caesarian section. China The Nei Ching, or Book of Medicine of the Yellow Emperor, probably written in the 3d century BC, describes human anatomy, including the circulation of the blood. Much of the treatment at that time was based on the yin-yang principle; that is, the balance between active and passive, hot and cold, male and female. The most important role of a Chinese physician was to restore the harmony between yin and yang in a patient. The Chinese also developed massage and invented \Tacupuncture\t and immunization against smallpox. The physician Hua T'o, in 300 BC, pioneered the use of anesthesia and performed abdominal surgery, including spleen removal. The Pen T'saokang-mu, begun in the 3d or 4th century AD and completed in the 16th century, describes about 1,000 drugs, including croton oil, opium, rhubarb, iron, and ephedrine, all of which have been used in modern times. The pinnacle of Chinese medicine was reached during the reign of Emperor \TCh'ien lung\t, when all medical information was compiled in a 40-volume encyclopedia, The Golden Mirror of Medicine (1743). Within a few years, however, European ideas began to be introduced, resulting in modern and traditional medicine simultaneously being practiced. Japan Little is known of Japanese medicine before the 7th century AD, when Chinese influence began to dominate medical practice. In the 1600s Western medicine was introduced by Portuguese missionaries. After Commodore Perry established contact, Japan rapidly advanced in medicine and science, and in the 20th century it became the equal of any nation. GREEK MEDICINE The healing art of ancient Hellenic people was associated with the worship of Apollo, for whom the Oracle at Delphi was established. According to legend, medicine, taught to Chiron by Apollo, was in turn passed on to Aesculapius, who may have been a real man who lived about 1200 BC, but later was thought to be a god and was worshiped in temples of healing. Inscriptions on these temples record the treatment of disease, consisting of rest, exercise, diet, and magic. Hippocrates \THippocrates\t was born on the Island of Cos in 460 BC. A great deal is known about this physician from about 70 books extant that were written either by him or by his students and followers. Among the more important principles he stressed were: (1) the physician should work not for personal gain but for love of humanity and should be sober, industrious, clean, discreet, and modest; (2) disease should be studied by meticulous observation, making use of sight, taste, touch, hearing, and smell in order to diagnose properly, and cases should be carefully recorded and studied to establish a prognosis; (3) disease is often the result of environmental forces--diet, climate, and occupation; and (4) the physician should emphasize simple treatment supplemented with careful diet and surgical intervention when necessary. A physician's conduct is summarized in the \THippocratic oath\t, sworn to by newly graduated physicians to this day. Aristotle In the 4th century BC, \TAristotle\t, pupil of Plato and teacher of Alexander the Great, dissected many species, studied insect and animal behavior with great accuracy, laid the foundations for embryology, and suggested evolution. Aristotle's importance was in his belief that the scientific method--careful observation, experimentation, and study of cause and effect-- could lead to greater scientific knowledge. ROMAN MEDICINE Roman medicine emphasized public health. Sanitation, sewage disposal, and the water system exceeded anything that followed in the Western world prior to the 19th century. Medical students were educated at public expense, and physicians were supplied for the poor and incorporated into the armed forces and hospitals. Celsus The most important contributions to medicine during the Roman Empire were those of \TCelsus\t and \TGalen\t. Aulus Cornelius Celsus (fl. AD 10-37), a Roman of patrician lineage, wrote an 8-volume encyclopedia on medicine known as De Re Medica. Little recognized during its own time, the work was rediscovered in the 15th century, at which time it had a great impact on scientific thought. Six of the eight books describe various diseases and discuss therapy using diet, drugs, and manipulation. The last two books treat topics in surgery, including operations for goiter, hernia, and bladder stone, as well as describing tonsillectomy and the removal of eye cataracts. Celsus also recommended treating fractures with splints and bandages stiffened with starch. Galen \TGalen\t (AD c.131-200), a Greek physician, served the emperor Marcus Aurelius. He wrote 500 books, 80 of which are extant. Although he stated that knowledge of human anatomy was fundamental for a physician, his anatomical facts were obtained from the dissection of animals and incorporated many errors when applied to human anatomy. Nevertheless, he explained the function of many nerves, discovered the sympathetic nervous system, and described almost all the structures of the brain visible to the naked eye. He insisted, however, that tiny pores existed in the heart through which blood passed from the right to the left ventricle, an error accepted throughout Europe for more than a thousand years. MEDICINE IN THE ISLAMIC EMPIRE Between the fall of Rome in the 5th century AD and the Renaissance in the 15th century, knowledge of medicine flourished in the Islamic empire. Islamic medicine was highly eclectic. That is, it combined elements of a number of other systems. It was strongly influenced by Greek medicine, knowledge of which came by means of Nestorian monks; by the medical writings of the Talmud; and by astrologic teachings from Egypt and the Orient to which addenda and commentaries were attached, especially concerning the use of drugs. The whole was codified in writing so that clinical trials could be evaluated to a limited extent. Basic chemical processes including distillation, crystallization, and sublimation, were discovered. Such Arabic words as aklaki, alcohol, syrup, and drug are now widely used. The great physicians of the Islamic world included, in the eastern caliphate, Rhazes (AD c. 860-930), a Persian who distinguished smallpox from measles, and \TAvicenna\t, the "Prince of Physicians," who was chief physician of the celebrated hospital in Baghdad. Avicenna's medical texts attempted the impossible; that is, he tried to codify all of medicine while squaring its facts with the systems of Galen and Aristotle. This melange nevertheless influenced European thought for centuries. In the western caliphate, under the Umayyad dynasty, the greatest clinicians were Avenzoar of Cordoba (d. 1162, in Seville) and \TMaimonides\t. Avenzoar was one of the few physicians in the centuries prior to the Renaissance with the courage to challenge the writings of Galen. Maimonides, a Jewish physician also of Cordoba, reacted to the increasing problems of being Jewish there and left for the greater freedom of the eastern caliphate, where he became Saladin's personal physician. Among his medical treatises is a text on hygiene that was highly influential. The Islamic civilization also established several hospitals. The greatest were the ones at Damascus (1160), which remained active for three centuries, and the Al-Mansur Hospital in Cairo (1276). The latter was the first hospital to emphasize science, teaching, and social service. It had separate wards for women, children, and convalescents, wards dedicated to specific diseases, an extensive library, and out-patient clinics. THE MEDIEVAL PERIOD IN EUROPE During the Middle Ages the influence of Christian theology affected medicine in several ways. The Christian emphasis on charity and concern for the sick and injured led to the establishment of hospitals often related to and maintained by monastic orders. In the later Middle Ages, spacious, fine hospitals were built by the Knights of St. John, including Saint Bartholomew's in London and one at Rhodes. The concern of Christian theology, on the other hand, was to cure the soul rather than the body; disease usually was considered supernatural in origin and cured by religious means. As a result, scientific investigation was inhibited during this time. Brothers of various monasteries copied and preserved those scientific manuscripts and documents which were thought to be consistent with prevailing religious thought, notably the works of Galen and Aristotle. Salerno The first European medical school was founded at Salerno, near Naples, in the 8th century. The area was still part of the Byzantine Empire, so that many Greek texts were available. The faculty derived its learning from several sources, and exceptional freedom was suggested by the probable presence of women professors; the best known, Trotula, was a gynecologist who published a handbook of midwifery. The anatomy taught there was based on that of the pig, and the physiology and pathology followed that of Galen, but a spirit of investigation suffused the institution. By the 11th century it had become a center of medical knowledge. The course of study took five years to complete, after which students were required to pass an examination before being allowed to practice. Although the school declined after the 12th century, its spirit was transmitted to the greatest medical schools of the Renaissance, Bologna and Padua. Montpellier A school was founded at Montpellier shortly after the one at Salerno. Intellectually descended from Islamic medicine, by the 13th century it was producing such physicians as Guy de Chauliac (c.1300-1370), one of the greatest of the medieval surgeons. That same century saw the founding of the schools at Bologna and Padua. At Bologna, the physician Taddeo Alderotti (c.1223-1303) was a prime mover in establishing postmortem dissections and an early developer of the Consilia, or medical case book, in which advice was given by the professor to younger or less sophisticated physicians. Thus was born the clinical case history. Medieval medicine was a mixture of magic, religion, and empirical investigation. This is exemplified by the varied reactions to the onset of the Black Death, or bubonic plague, which first appeared in Europe in 1348. The plague was ascribed to miasmas, vapors, poisoning of wells by Jews, divine punishment for sins, and as many other reasons as fertile imaginations could devise. On the other hand, a good medical description of the disease was provided by de Chauliac, and the plague's visitation resulted in the appointment of three guardians of public health by the Venetian Republic--the first such public health officers. MEDICINE OF THE RENAISSANCE PERIOD The Renaissance revolutionized medical thought as it did all scientific, artistic, and other intellectual activity. The dissemination of knowledge was greatly aided by the development of printing. Andreas \TVesalius\t, born in Brussels, was a professor of \Tanatomy\t in Padua, where he wrote De Humani Corporis Fabrica (On the Fabric of the Human Body, 1543). This work was the first accurate anatomy text and included masterful illustrations that corrected errors of Galen. Vesalius was the first of a line of superb anatomists at Padua, among whom were Hieronymus \TFabricius\t and Gabriel Fallopius. Ambroise \TPare\t, a French physician, revolutionized surgery. He treated his patients humanely, using ligatures to stop bleeding from vessels instead of cauterizing them with boiling oil or hot instruments. Other men of this age included Aureolus \TParacelsus\t, a Swiss physician who rejected traditional schools of thought and advocated the use of such chemicals as laudanum (a preparation of opium) in the treatment of disease. Girolamo \TFracastoro\t, an Italian physician, is best known for his work on syphilis and other infectious diseases. THE SEVENTEENTH CENTURY William \THarvey\t, an English physician of the 17th century, studied in Padua under Fabricius and later taught anatomy in London. He published De Motu Cordis (On the Motion of the Heart, 1628), which describes the circulation of blood throughout the body. As the first application of the idea of measurement to a biological phenomenon, the book exhibited true science in its solution of a medical problem. Its importance was quickly recognized by Harvey's contemporaries. The Galenic idea that the heart was a source of heat and that the lungs were cooling devices for the heart gave way before the elegant experiments of English scientists Richard Lower (1631-91) and John Mayow (1640-79). Mayow passed venous blood through lungs and showed that the change from dark to bright red was associated with the uptake of some substance from the air--an observation all the more remarkable in that the substance, oxygen, had not yet been discovered. Perhaps the greatest clinician of the century was Thomas \TSydenham\t, who showed concern for the effects of environmental factors on health and had a humanistic approach to the treatment of patients. His written works on fevers and gout are classics of clinical detail and accuracy. The century was also remarkable for the invention and development of the microscope. By using the microscopes, a Dutch scientist, Antoni von \TLeeuwenhoek\t, discovered red blood cells, bacteria, and protozoa as well as describing the microscopic appearance of muscle. The greatest microscopist of the century, Marcello \TMalpighi\t, described the embryology of the chick and was the first to observe capillaries, although it was Leeuwenhoek who realized that capillaries completed Harvey's postulated circulation of the blood. Two philosophic schools of medicine arose in the century both of which contributed to science but also slowed progress by their excessive rigidity. One, the iatrophysical school, regarded all physiological events as the rigid results of the laws of physics. The mathematician Rene Descartes subscribed to this school, but its greatest exponent was Italian scientist Giovanni \TBorelli\t. Many of his studies were valid, but he also advanced such notions as that digestion was a purely mechanical process of grinding and crushing. The iatrochemical school, founded by Flemish chemist Johannes Baptista von \THelmont\t, began as a jumble of ill-defined notions. The idea of the importance of chemistry in medicine, however, took on significance when propounded by English physicist Thomas Willis (1621-75), who analyzed urine in detail and noted the presence of sugar in diabetic urine. Similarly, Dutch physician Regnier de Graaf (1641-73) collected pancreatic juice and recognized its importance in the digestion of food by chemical rather than mechanical means. Along with the growth of medical science, an extraordinary amount of humbug was promulgated. Schools of therapeutics based on the "doctrines" of the Egyptian god Thoth and on Zoroastrian or Rosicrucian teachings were widely respected by royal courts. Because of the growing appreciation of the fact that correct medical therapy was based on reasons that could in time be found through research, it was easy for persons to develop false systems that had sufficient logic to give them a flavor of science and therefore of validity. The great schools of medicine in the 17th century were those of Leyden, Paris, and Montpellier. During this period the Royal Society of London, the Academie des Sciences in Paris, and the Collegium Naturae Curiosorum in Germany were founded and dedicated to the advancement of science. By means of these societies ideas were exchanged and journals published, thus spreading information throughout much of Europe. THE EIGHTEENTH CENTURY During the 18th century Georg Ernst \TStahl\t, professor of medicine at Halle and the developer of the phlogiston theory in chemistry, postulated that movement in all living systems resulted from the presence of what he called anima, or the soul. This theory was refined by a French physician, Paul-Joseph Barthez (1734-1806), who suggested that all living forms possessed a nonmaterial elan vitale, or "life force." The concept was not completely rejected as a scientific theory until Eduard \TBuchner\t and his brother showed that yeast fermentation of sugar could occur using only the filtered juice of ground-up yeast. It was then conceded that the process exhibited a function of living systems but did not involve life. Theories of Treatment Various humbug systems of the preceding century became more polished and subtle in the 18th century. For example, following the "life force" school of thought, John Brown (1735-85) of Edinburgh concluded that all disease was due to excessive stimulation or lack of stimulation. He developed the Brunonian system of treating disease, administering either sedatives or stimulants in massive doses. Because the basis of the method of treatment was wrong, much harm was done to patients. Battles over the Brunonian system were bitter, even resulting in riots. An equally all-inclusive system, but one opposite to that of Brown, was developed by Samuel Hahnemann (1755-1843). He advocated treating the patient with a drug that produces the same symptoms as the disease from which he or she is suffering. This practice might have had disastrous consequences had it not been for his second principle, which stated that the smaller the dose, the more effective the drug. As a result his patients were prescribed harmless medicines. Hahnemann also insisted that drugs be given separately rather than in dangerous mixtures that were in vogue for centuries. His system, called \Thomeopathy\t, led to the establishment of homeopathic medical schools, hospitals, and societies worldwide, a movement that virtually disappeared in the 20th century. Medical Advances Hermann \TBoerhaave\t, a Dutch physician, by means of his practice, teaching, and writings, influenced the development of Leiden into the world center for medicine. James \TLind\t, a British naval surgeon, cured scurvy, caused by a deficiency of vitamin C, by requiring sailors to drink lime and lemon juice. Edward \TJenner\t demonstrated that vaccination with cowpox, a mild disease, would prevent smallpox. Smallpox has been eradicated as a result. English physician William Withering (1741-99) discovered the use of digitalis, perhaps the most useful drug in the treatment of heart disease. Austrian physician Leopold Auenbrugger (1722-1809) found that by tapping gently on the chest, fluid in the chest cavity as well as other signs of disease could be detected. English surgeon John Hunter (1728-93) is notable for his emphasis on precise anatomical knowledge and his insistence on experimentation. Italian anatomist Giovanni B. Morgagni (1682-1771) founded pathologic anatomy, and French physiologist Marie Francois Bichat (1771-1802) developed histology. THE NINETEENTH CENTURY Preceding the 19th century, medicine had advanced at a slowly increasing rate; the scientific basis of practice, however, aside from anatomy, was created during the 19th century. The basic medical sciences were founded, opening the way for immense strides in clinical practice during the 20th century. Advances in Medical Science During the 19th century Jakob \THenle\t showed that the kidney contained tiny tubules responsible for the urine-forming function of that organ. His descriptions of the microscopic structure of the eye and brain also led to consideration of the relationship of structure (anatomy) to function (physiology). Rudolf \TVirchow\t, the founder of cellular pathology, was responsible for promoting the use of the microscope. He demonstrated that all body tissues and organs are made of cells and their products, that all cells are produced from other cells, that many diseases were the result of changes in cells, and that one could identify a disease by the appearance of the cells. His work became the basis for modern-day understanding of disease. The science of microbiology was founded by Louis \TPasteur\t, who trained as a chemist and became interested in the chemical basis for fermentation. In his chemical work Pasteur showed that certain pure chemical crystals could exist in two forms, differing from each other as an object differs from its mirror image. The importance to medicine of this work is that the building blocks of the body, such as amino acids and sugars, are usable in one form only and not in mirror-image form. Pasteur conducted a series of complex experiments proving that many plant and animal diseases are due to yeasts and bacteria. He discovered methods of immunization, a process that has saved more lives than all advances in all of previous medicine. Further, his work, developed by others after him, has resulted in safe milk (through pasteurization) and food, better methods of producing chemicals and drugs, and increased agricultural production. The science of bacteriology developed rapidly in the last quarter of the 19th century, when the bacteria causes of many important diseases were identified. The greatest of the numerous scientists working in this field was Robert \TKoch\t, who along with Pasteur is considered the founder of scientific bacteriology. Koch isolated the organisms that produce anthrax, tuberculosis, and cholera, and invented the gel-like medium used for many years on plates in bacteriology laboratories (a substance now replaced by agar). He also developed a set of rules (Koch's postulates) that, if followed, can prove that an organism is truly the cause of a disease rather than simply having been found in a sick person. The Rise of Modern Surgery The 19th century made modern surgery possible by means of two great discoveries: safe anesthesia, and control of wound infection. A Boston dentist, William \TMorton\t, discovered that inhalation of diethyl ether would render a person unconscious and incapable of perceiving pain. He demonstrated his discovery at the Massachusetts General Hospital in 1846 by making it possible for a leading Boston surgeon, John C. Warren, to operate on an unconscious patient (see \Tanesthetics\t). As surgeons began using anesthesia to perform longer, more intricate operations, however, the benefits of Morton's discovery began to be diminished by wound infections, or sepsis, caused by the entrance of bacteria into the bloodstream. In Vienna, Hungarian physician Ignaz \TSemmelweis\t had been insisting that puerperal sepsis, a usually fatal infection experienced by some women after childbirth, was due to infection of the birth canal by the hands of hospital attendants. This theory was ridiculed, because at the time no scientific reason was known that supported it. When Pasteur showed that microorganisms in the air and on hands could produce disease, however, the British surgeon Joseph \TLister\t began his epochal work on infection. Published in 1867, this work showed that surgery was made safer by using antiseptics such as phenol to sterilize equipment and the surrounding environment. The antiseptic process was thereafter gradually extended to make the operating room germ free by sterilizing all equipment and supplies, covering surgeons and attendants with sterile gowns, and draping the patient so that only the site of actual operation is exposed. The consequences for surgery were enormous. Physical Diagnosis The process of diagnosis, which involves taking a patient's medical history and then conducting a careful examination, was perfected in the 19th century. Most notable in this development was the Viennese school of so-called nihilists, who felt that what was then known of therapy was so poor that the brightest physicians should devote themselves to diagnosis rather than employ invalid therapy. Whatever the merits of this stance, its leading exponent, the Czech physician Joseph Skoda (1805-81), laid the groundwork for the diagnostic process as it is known today. Psychiatry The roots of modern \Tpsychiatry\t extend to the very last years of the 18th century, when French physician Philippe Pinel (1745-1826) was beginning to alter the treatment of persons suffering from psychoses. Such patients had been incarcerated in institutions and chained to walls until, in 1798, Pinel removed chains from patients at the Bicetre Hospital in Paris and began to popularize the concept of psychotics as patients and psychiatry as a field of medicine rather than a branch of penology. These enlightened attitudes developed until, by the last quarter of the 19th century, psychiatry was dominated by two figures: Emil \TKraepelin\t in Germany and Sigmund \TFreud\t in Vienna. Kraepelin's work was important in demonstrating that the discipline of psychiatry could be subjected to the same rigorous standards of investigation as other medical disciplines, while Freud revolutionized understanding of the unconscious mind and the treatment of sufferers from neuroses and anxiety. Freud's concept of the role of the unconscious and the significance of dreams affected not only psychiatry and the rest of medicine thereafter but also anthropology, sociology, and the arts. THE TWENTIETH CENTURY Medicine in the 20th century made enormous advances in the basic medical sciences. It also expanded to take full advantage of the equally rapid strides being made in all the other fields of science and technology. As a result, no synopsis of the achievements of medicine in the century can really be provided here. Individual entries on the various fields of medicine provide such current reviews. Antibiotics One major area of advance in 20th century medicine has been in pharmaceuticals, and in particular the development of \Tantibiotics\t. Pioneering in this field, German bacteriologist Paul \TEhrlich\t began his career by discovering that many cells would bind to specific dyes then being developed by the German chemical industry. In this way he discovered certain of the body's white blood cells and was able to stain the tubercle bacillus, a crucial step in identifying the tuberculosis-causing organism and developing means of controlling the disease. In 1909, Ehrlich synthesized arsphenamine, a drug that could destroy the syphilis-causing organism Treponema pallidum. With this accomplishment, Ehrlich ushered in the age of antibiotics and chemotherapy. His concern that molecules would adhere to one another if their shapes were complementary also became one of the basic concepts of immunology as well as of general body chemistry. The German physician Gerhard \TDomagk\t, working 25 years after Ehrlich, developed the first useful \Tsulfa drug\t, or sulfonamide, which was used to treat streptococcal disease. In 1929 the British bacteriologist Alexander \TFleming\t discovered \Tpenicillin\t, which destroys various bacteria. During the stress of World War II the drug was purified, manufactured on a huge scale, and shown to be safe and effective in treating a host of diseases, including gonorrhea, syphilis, and meningitis. In 1943 the microbiologist Selman \TWaksman\t discovered streptomycin, the first antibiotic effective against tuberculosis; it was also effective against a number of other bacteria not affected by penicillin. Many antibiotics are now in use, one or the other of them efficacious against most of the bacterial infections found in patients with a normal immune system. Vaccines The 20th century has seen the conquest of a number of diseases through immunization. Smallpox, as noted, has disappeared worldwide. In technologically advanced countries a number of childhood diseases such as poliomyelitis, rubeola (measles), rubella (German measles), diphtheria, and mumps now occur infrequently and sporadically. Vaccines against diseases such as influenza have also been developed, but influenza and a number of others remain difficult to control because of the many varieties of the virus and its capacity to mutate. Such difficulties surround current research on a vaccine against the deadly acquired immune deficiency syndrome (see \TAIDS\t). Research medicine is thus heavily involved in efforts to understand the immune system, not only with respect to \TAIDS\t but also because of other diseases such as rheumatic fever, rheumatoid arthritis, and lupus erythematosus. Also, because many cancer cells have been shown to be capable of combining with unique antibodies, the possibility exists that at least some cancers may ultimately be dealt with through immune-related methods such as vaccines. Medical Genetics Medical research at the cellular level, such as on the immune system, has been made possible through 20th-century advances in genetic techniques. The causes of many diseases have been traced to defective chromosomes or to specific genes on the chromosomes. The hope is that such diseases can eventually be treated through direct intervention, using the techniques of \Tgenetic engineering\t. By means of such techniques, several natural body chemicals have become available in quantity, including insulin, interferon, clot-dissolving enzymes, and human growth hormone. Medical researchers have also proposed the eventual mapping of the entire human \Tgenome\t. Medical Technology The contributions of other fields of science and technology to advances in 20th-century medicine and surgery have been so numerous that only one such field can be chosen as an example. That is, the discovery of X rays led rapidly to their employment in various diagnostic and therapeutic ways, and their use in medical research made possible the elucidation of the structure of molecules such as \TDNA\t, proteins, and vitamins. Basic medical science has also become significantly dependent on the use of radioactive isotopes, by means of which various biosynthetic processes and the degradation of biochemicals within the body can be elucidated. Such isotopes have also made possible the detection and quantification of molecules that are present in body tissues in such minute concentrations that they could not otherwise be measured. Modern diagnostic tools now include a wide range of advanced devices. Aaron D. Freedman, M.D. Bibliography: Ackerknecht, E. H., A Short History of Medicine, rev. ed. (1982); Castiglioni, Arturo, A History of Medicine, trans. by E. B. Krumblhaar, 2d ed. (1947; repr. 1973); Duffy, John, The Healers: A History of American Medicine (1976); Keen, Harry, et al., Triumphs of Medicine (1976); Klavans, H. L., The Medicine of History: From Paracelsus to Freud (1982); Kohn, Alexander, False Prophets: Fraud, Error and Misdemeanour in Science and Medicine (1987); Leavitt, J. W., and Numbers, R. L., eds., Sickness and Health in America: Readings in the History of Medicine and Public Health (1985); McGrew, Roderick, Encyclopedia of Medical History (1984); Majno, Guido, The Healing Hand (1975); Ravitch, M. 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