Darwin, Pasteur, and Koch
The theory of evolution put forward by Charles Darwin revived interest in the science of comparative anatomy and physiology; the plant-breeding experiments of the Austrian biologist Gregor Johann Mendel had a similar effect in stimulating studies in human genetics and heredity.
The early studies of the French chemist and microbiologist Louis Pasteur of fermentation resulted in the final destruction of the concept of spontaneous generation and brought about a revival of interest in the theory that disease might be the result of a specific contagium. Important in the development of the germ theory was the pioneering work in puerperal fever of the American doctor and author Oliver Wendell Holmes and of the Hungarian obstetrician Ignaz Philipp Semmelweis, who showed that the high rate of mortality in women after childbirth was attributable to infectious agents transmitted by doctors' unwashed hands.
Pasteur and the German doctor and bacteriologist Robert Koch are usually given equal credit for their contributions to bacteriology; the development of this field is generally considered the greatest single advance in the history of medicine. Within a few decades the causes of such age-old scourges as anthrax, diphtheria, tuberculosis, Hansen's disease (leprosy), and plague were isolated. The German physiologist Emil Heinrich Du Bois-Reymond added new knowledge by his studies of metabolic processes and of the physiology of muscles and nerves.
Bacteriology and Surgery
Some early bacteriologists were: the German physiologist Edwin Theodore Albrecht Klebs, who found the bacillus causing diphtheria, researched the bacteriology of anthrax and malaria, and produced tuberculosis in cattle and syphilis in apes; the German bacteriologist Friedrich August Johannes Löffler, who discovered the bacterium of gonorrhoea; and the Norwegian doctor Gerhard Henrik Hansen, who discovered the leprosy bacillus. The German gynaecologist Karl Sigismund Franz Credé developed the method of placing drops of an antiseptic solution of silver nitrate in the eyes of the newborn to prevent gonorrhoeal ophthalmia. Pasteur's method of immunization by injecting attenuated virus was used successfully in the treatment of rabies, and the German bacteriologist Emil Adolph von Behring developed immunizing serums against diphtheria and tetanus. The Russian bacteriologist Élie Metchnikoff was the first to demonstrate the phagocytic, or bacteria-destroying, property of certain white cells in the blood (the process of phagocytosis).
Surgery derived important benefit from the development of the germ theory. The British surgeon and biologist Joseph Lister adopted the use of carbolic acid as an antiseptic agent with impressive results in reducing mortality from wound infection. Lister's demonstrations that bacteria are airborne were later expanded to a realization that they are also carried by the hands and by instruments, the sterilization of which introduced the era of aseptic surgery. Another great advance in surgery came with the discovery of anaesthetics.
Physiology
X-Ray Since its accidental discovery in 1896, the X-ray has been a vital diagnostic and therapeutic tool. Produced by bombarding a target made of tungsten with high-speed electrons, X-rays are absorbed by dense bone and pass through the soft tissue of internal organs. On a photographic plate, bone appears white and soft tissues appear grey. While diagnostic dental and medical X-rays are low-intensity beams, high-intensity X-rays, capable of destroying tissue, are used in the treatment of tumours. Rapidly dividing cancerous cells are especially vulnerable to X-rays.Omikron/Science Source/Photo Researchers, Inc.
With progress in physics and chemistry, the science of physiology made tremendous strides during the 19th century. Among outstanding physiologists of this period were the German chemist Justus von Liebig, who developed analytical methods of organic chemistry and studied food chemistry and metabolism, and the German physicist and physiologist Hermann Ludwig Ferdinand von Helmholtz, who invented the ophthalmoscope and ophthalmometer, investigated the speed of nerve impulses and reflexive processes, and performed studies of primary importance in optics and acoustics. The French physiologist Claude Bernard, recognized as the founder of experimental medicine, made important discoveries about the functions of the pancreas and the liver, and about the sympathetic nervous system. The Russian physiologist Ivan Petrovich Pavlov, who elaborated the theory of the conditioned reflex, the basis of behaviourism, developed Bernard’s work on the interaction of the digestive system and the vasomotor system, which controls the size of blood vessels, further.
Other physiologists of the 19th century include the French-American doctor and physiologist Charles Édouard Brown-Séquard, who investigated the activities of the various glands composing the endocrine system, and Carl Friedrich Wilhelm Ludwig, a German physiologist, who explored cardiac and renal activity through new methods of functional study. The work of the Spanish histologist Santiago Ramón y Cajal contributed new knowledge of the structure and function of the nervous system.
Another valuable diagnostic aid was the X-ray, discovered accidentally by the German physicist Wilhelm Conrad Roentgen. The Danish doctor Niels Ryberg Finsen developed an ultraviolet-ray lamp, which led to an improved prognosis for tuberculosis of the skin and other skin diseases (see ultraviolet radiation). The discovery of radium by the French physicists Pierre Curie and Marie Curie offered a treatment for some forms of cancer.
In 1803 the American biologist John Richardson Young described the process of acid formation in gastric digestion. Thirty years later the American surgeon William Beaumont published his remarkable studies on the gastric juices and the physiology of digestion based on his observations of a patient suffering from a gastric fistula. In the field of operative gynaecology, the American doctor and surgeon Ephraim McDowell performed the first surgical removal of an ovarian tumour in 1809, and the gynaecologist James Marion Sims saved the lives of countless women by his surgical correction of vesicovaginal fistula (opening from the bladder into the vagina), first performed in 1845.
In 1900 the United States Army doctor, surgeon, and bacteriologist Walter Reed and his colleagues, acting on a suggestion made by the Cuban biologist Carlos Juan Finlay, demonstrated that the mosquito is the vector of yellow fever only a few years after the British doctor Ronald Ross had proved the role of the mosquito as a carrier of the malarial parasite.