In the 19th century, sound scientific thinking and new medical technologies led to advances in every area of medicine, particularly the eradication of many of the world's worst diseases. Of fundamental importance was the discovery of a connection between filth and disease, and public acceptance of the theory led to improved sanitation and other public health measures. Independently established by Louis Pasteur and Robert Koch in the 1870s, the germ theory of disease, which holds that bacteria and other microbes cause and spread infectious diseases, enabled scientists to isolate the causative agents of diphtheria, tuberculosis, and other scourges, leading to the development of vaccines. In 1879, Pasteur accidentally discovered that bacteria could be weakened, which prevents them from causing disease but still enables them to trigger immunity in infected individuals. Using weakened anthrax bacteria taken from the blood of diseased animals, Pasteur developed the first artificially produced vaccine in 1881. Vaccines for rabies (1885), cholera (1893), plague (1897), and typhoid (1897) soon followed.
Many new drugs were developed at this time, including acetylsalicylate, a derivative of the active ingredient in willow bark, a remedy used for combating fever for more than 2,000 years. Now known as "aspirin," it went on the market in 1899 after development by the German pharmaceutical company Bayer. Other drugs to appear in the physician's medicine cabinet included digitalis for heart ailments, amyl nitrate for angina, quinine for malaria, and sedatives such as chloral hydrate and paraldehyde.
Scientists of the era discovered that all organisms are composed of cells, determined the functions of nerves and certain parts of the brain, showed the role of the liver in carbohydrate metabolism, and carefully described numerous diseases for the first time. In 1819, the French physician Rene Laennec invented the stethoscope, which was used to listen to the lungs and heart, allowing physicians to hear for the first time "the cry of the suffering organs." Until the 1860s, doctors used long thermometers to take a patient's temperature, a process that took almost 20 minutes. In 1866, Thomas Allbutt introduced the short, clinical thermometer, the use of which was advanced by Carl Wunderlich, who showed that fever is a symptom, not a disease. In 1895, Wilhelm Conrad Rontgen made the first "medical" X-ray, named for a then unknown type of radiation, which for the first time enabled doctors to see inside the body without surgery.
Modern surgery emerged in the 19th century as well. Physicians recognized the three major obstacles to successful surgery -- pain, infection, and bleeding. Two American dentists, Horace Wells and William Morton, discovered anesthesia in the 1840s. By reducing the trauma of surgery for patients, anesthesia allowed doctors to take more time over their work and to apply surgery to more ailments.
In 1867, the British surgeon Joseph Lister popularized antiseptic surgery and sterilized equipment, and the practice dramatically reduced infections in surgery patients and improved the odds of survival. Around 1890, William Halsted introduced the practice of wearing sterilized rubber gloves during surgery. By the end of the 19th century, the age-old practice of bloodletting was finally abandoned. The modern blood-type classification system, used to replenish a patient's blood through transfusions, began with the 1900 discovery of the ABO blood groups by the Austrian scientist Karl Landsteiner.
Not all medical milestones were achieved in laboratories and operating rooms. In 1889, William Osler was appointed the first physician-in-chief at John's Hopkins Hospital in Baltimore, where he revolutionized the way the medical curriculum was taught. Osler insisted that students learn at the bedside, implementing his belief that "the good physician treats the disease; the great physician treats the patient who has the disease." Students took patient histories, conducted physical examinations, and studied laboratory results, leading to a more interactive and humane treatment of medical conditions. Osler established the medical residency, in which doctors in training make up much of a hospital's medical staff. This system remains in place today in most teaching hospitals.
In the 20th century, advances in medicine came rapidly, changing the nature of death's threat. When the 20th century began, life expectancy in the United States was 47 years. In 2000, the average life span had increased to almost 77 years. The dramatic decline in the mortality rate is in large part due to the advancement of medicine, as well as the development of drugs to combat infectious diseases.
In 1901, Walter Reed, a U.S. Navy pathologist, discovered that viruses could cause disease in humans. His experiments proved that yellow fever was caused by a virus transmitted by mosquitoes. Development of electron microscopes in the 1930s gave scientists their first glimpse of viruses, and tissue culture techniques enabled researchers to grow viruses in the laboratory for drug testing, preparation of vaccines, and other purposes.
Another type of disease-causing agent, distinct from viruses, was first isolated in 1982. Called prions, these particles consist of a single protein; they can be transformed into abnormal shapes capable of destroying cells. Prions cause spongiform encephalopathies, fatal diseases characterized by the breakdown of brain tissue -- the most famous of which is commonly known as mad cow disease.
Hormones were isolated in 1901, and the therapeutic use of hormones began 20 years later when insulin, a hormone produced by certain pancreatic cells, was injected into a person with diabetes, a disease that slows or stops the body's natural production of insulin.
Perhaps the most significant contribution in the field of endocrinology came 50 years later, with the creation of the birth control pill. In the early 1950s, Gregory Pincus, an American biologist and researcher, discovered that injections of the hormone progesterone would inhibit ovulation and prevent pregnancy. Seed money for this effort was provided by Margaret Sanger, a lifelong advocate for women's rights. At the same time, Carl Djerassi created an orally effective form of synthetic progesterone. It was another decade before "the pill" received F.D.A. approval and became commercially available, ushering in both a medical and social revolution.
In the first decade of the 20th century, scientists realized that certain "accessory food factors" are essential to good health. In 1911, Casimir Funk (1884-1967) found the first of these factors, B, and in a 1912 paper proposed the factors be called vitamins. Soon after the discovery of vitamins A (1913), D (1922), E (1922), C (1928), and K (1934), these substances soon became widely available.
Paul Ehrlich (1854-1915), a German scientist, helped found modem chemotherapy -- the use of chemicals to fight disease -- a treatment that proved effective against diseases that did not respond to serum therapy. He began to work with substances that killed or inhibited the growth of parasites, and in 1910 he successfully synthesized Salvarsan, the "magic bullet" used to cure syphilis.
Medicine was revolutionized in 1928, when Alexander Fleming discovered the antibiotic properties of penicillin, but he was unable to produce it in a form pure enough to use on patients. Ten years later, Howard Florey and others at Oxford University solved this problem, and by World War II techniques were developed in the United States for the commercial production of the drug. Its disease-fighting potential was recognized in the early years of World War II, and it saved the lives of countless wounded soldiers. Today a number of penicillins are available, and they are among the most widely used antibiotics.
In 1900, pneumonia and tuberculosis were the leading causes of death in the United States, but by 2000 these and most other common bacterial infections had been brought under control, although scientists now recognize that microorganisms have the ability to develop a resistance to these medications.
Genetics, as a distinct field of study, came to prominence in 1900, when three botanists independently rediscovered the basic laws of heredity published by Gregor Mendel in 1866. By 1911, Thomas Hunt Morgan (1866-1945) had discovered that mutations could occur in genes, and by the 1940s scientists had established that all organisms as well as viruses can mutate.
In the early 20th century, surgeons began to specialize and new fields emerged, building on the efforts of a few extraordinary individuals. Not for the first time, the theater of war made an enormous contribution to the progress of medicine. Harold Gillies, a New Zealand-born, British Red Cross doctor in World War I, saw that while soldiers could survive their battle wounds, surgeons had neither the skill nor the time to deal with their often dramatic disfigurements. Gillies devoted himself to the study and practice of plastic surgery, founding Queen's Hospital in Kent, England, where more than 10,000 reconstructive surgeries were performed. The techniques he invented, including skin grafts, were adopted by surgeons around the world and ushered in the era of reconstructive and, ultimately, cosmetic surgery.
Working in some of America's finest hospitals, including John's Hopkins Hospital in Baltimore and Peter Bent Brigham Hospital in Boston, Harvey Cushing emerged as the first true neurosurgeon in the early 20th century. Among his many innovations, Cushing created a way to stem the flow of blood with clamps and cuffs, minimizing the possibility that the patient would bleed to death. He pioneered the use of the "electric scalpel" and demanded that his team work with masks and gloves to minimize infection. His patients were the first to receive around-the-clock nursing care after surgery, and this type of postoperative treatment was the forerunner of intensive care units. Taken together, Cushing's contributions made brain surgery safer and more effective.
Other surgical milestones during this period included the first successful appendectomies, performed in Davenport, Iowa, in 1885 by Dr. William West Grant, and at roughly the same time by Dr. H. Hancock in England. In 1932, the American surgeon Michael E. DeBakey developed a roller pump that became an essential component of the heart-lung machine, which enabled the first open-heart surgery, performed by John H. Gibbon, Jr. in 1953. In 1966, DeBakey implanted the first mechanical heart in a human, and the successful transplantation of the liver (1963), lung (1963), pancreas (1966), intestine (1966) soon followed. In 1967, Dr. Christiaan Barnard performed the first successful human heart transplant. Bone marrow transplants began in 1964, and today stem cell transplants represent one of the most exciting-and controversial-frontiers in modern surgery. In 1990, the so-called laparoscopic technique was perfected, allowing surgeons to make much smaller incisions in the patient's abdomen to remove small organs through the navel.
Twentieth-century technologies such as computers, electronics, fiber optics, lasers, and ultrasound were all incorporated into medicine, making diagnosis more accurate and treatments safer. Mammography for diagnosing breast cancer was introduced in 1913 and the electroencephalograph (EEG) for recording brain waves in 1929. The heart can be monitored by recording electrical activity via skin electrodes with an electrocardiography (EKG) machine; magnetic resonance imaging (MRI) greatly improved the imaging provided by X-rays. A CAT scan combines X-ray equipment with computers that create detailed images of body tissue, allowing for greater ease in tough diagnoses.
Great advances also occurred in the construction of artificial body parts: aluminum, titanium, plastic resins, and three-dimensional computer modeling are used to build sophisticated limbs and joints.
Through the past millennia, the human life span has increased as people have learned how to prevent and treat illness, although in spite of medical advances, humans continue to face major health challenges. While many infectious diseases have been brought under control, AIDS, Lyme disease, and other emerging diseases discovered only in recent decades have created new medical battlefields. As people live longer, there is a growing incidence of arthritis, Alzheimer's disease, and heart failure. However, a better understanding of human biology, genetics, and psychology has led to improved preventive measures, diagnostic tools, and therapies.
(‘The New York Times ‘Smarter by Sunday – 52 Weekends of Essential Knowledge for the Curious Mind’)