The 100 Most Influential Scientists of All Time (24 page)

As Pasteur showed further, one component of the racemic acid (that identical with the tartaric acid from fermentation) could be utilized for nutrition by microorganisms, whereas the other, which is now termed its optical antipode, was not assimilable by living organisms. On the basis of these experiments, Pasteur elaborated his theory of molecular asymmetry, showing that the biological properties of chemical substances depend not only on the nature of the atoms constituting their molecules but also on the manner in which these atoms are arranged in space.

In 1854 Pasteur became dean of the new science faculty at the University of Lille, where he initiated a highly modern educational concept: by instituting evening classes for the many young workmen of the industrial city, conducting his regular students around large factories in the area, and organizing supervised practical courses, he demonstrated the relationship that he believed should exist between theory and practice, between university and industry. At Lille, after receiving a query from an industrialist on the production of alcohol from grain and beet sugar, Pasteur began his studies on fermentation.

From studying the fermentation of alcohol he went on to the problem of lactic fermentation, showing yeast to be an organism capable of reproducing itself, even in artificial media, without free oxygen—a concept that became known as the Pasteur effect. He later announced that fermentation was the result of the activity of minute organisms and that when fermentation failed, either the necessary organism was absent or was unable to grow properly. Pasteur showed that milk could be soured by injecting a number of organisms from buttermilk or beer but could be kept unchanged if such organisms were excluded.

As a logical sequel to Pasteur's work on fermentation, he began research on spontaneous generation (the concept that bacterial life arose spontaneously), a question which at that time divided scientists into two opposing camps. Pasteur's recognition of the fact that both lactic and alcohol fermentations were hastened by exposure to air led him to wonder whether his invisible organisms were always present in the atmosphere or whether they were spontaneously generated. By means of simple and precise experiments, including the filtration of air and the exposure of unfermented liquids to the air of the high Alps, he proved that food decomposes when placed in contact with germs present in the air, which cause its putrefaction, and that it does not undergo transformation or putrefy in such a way as to spontaneously generate new organisms within itself.

After laying the theoretical groundwork, Pasteur proceeded to apply his findings to the study of vinegar and wine, two commodities of great importance in the economy of France; his pasteurization process, the destruction of harmful germs by heat, made it possible to produce, preserve, and transport these products without their undergoing deterioration.

In 1865 Pasteur undertook a government mission to investigate the diseases of the silkworm, which were about to put an end to the production of silk at a time when it comprised a major section of France's economy. To carry out the investigation, he moved to the south of France, the centre of silkworm breeding. Three years later he announced that he had isolated the bacilli of two distinct diseases and had found methods of preventing contagion and of detecting diseased stock.

In 1870 he devoted himself to the problem of beer. Following an investigation conducted both in France and among the brewers in London, he devised, as he had done for vinegar and wine, a procedure for manufacturing beer that would prevent its deterioration with time. British exporters, whose ships had to sail entirely around the African continent, were thus able to send British beer as far as India without fear of its deteriorating.

By 1881 Pasteur had perfected a technique for reducing the virulence of various disease-producing microorganisms, and he had succeeded in vaccinating a herd of sheep against the disease known as anthrax. Likewise, he was able to protect fowl from chicken cholera, for he had observed that once animals stricken with certain diseases had recovered they were later immune to a fresh attack. Thus, by isolating the germ of the disease and by cultivating an attenuated, or weakened, form of the germ and inoculating fowl with the culture, he could immunize the animals against the malady. In this he was following the example of the English physician Edward Jenner, who used cowpox to vaccinate against the closely related but more virulent disease smallpox.

On April 27, 1882, Pasteur was elected a member of the Académie Française, at which point he undertook research that proved to be the most spectacular of all—the preventive treatment of rabies. After experimenting with inoculations of saliva from infected animals, he came to the conclusion that the virus was also present in the nerve centres, and he demonstrated that a portion of the medulla oblongata of a rabid dog, when injected into the body of a healthy animal, produced symptoms of rabies. By further work on the dried tissues of infected animals and the effect of time and temperature on these tissues, he was able to obtain a weakened form of the virus that could be used for inoculation.

Having detected the rabies virus by its effects on the nervous system and attenuated its virulence, he applied his procedure to man; on July 6, 1885, he saved the life of a nine-year-old boy, Joseph Meister, who had been bitten by a rabid dog. The experiment was an outstanding success, opening the road to protection from a terrible disease.

(b. Jan. 8, 1823, Usk, Monmouthshire, Wales—d. Nov. 7, 1913, Broadstone, Dorset, Eng.)

A
lfred Russel Wallace was a British humanist, naturalist, geographer, and social critic. He became a public figure in England during the second half of the 19th century, known for his courageous views on scientific, social, and spiritualist subjects. His formulation of the theory of evolution by natural selection, which predated Charles Darwin's published contributions, is his most outstanding legacy, but it was just one of many controversial issues he studied and wrote about during his lifetime. Wallace's wide-ranging interests—from socialism to spiritualism, from island biogeography to life on Mars, from evolution to land nationalization—stemmed from his profound concern with the moral, social, and political values of human life.

Wallace was an enthusiastic amateur naturalist with an intellectual bent, and he read widely in natural history, history, and political economy. Inspired by reading about organic evolution in Robert Chambers's controversial
Vestiges of the Natural History of Creation
(1844), unemployed, and ardent in his love of nature, Wallace and his naturalist friend Henry Walter Bates, who had introduced Wallace to entomology four years earlier, traveled to Brazil in 1848 as self-employed specimen collectors. Wallace and Bates participated in the culture of natural history collecting, honing practical skills to identify, collect, and send back to England biological objects that were highly valued in the flourishing trade in natural specimens.

Wallace spent a total of four years traveling, collecting, mapping, drawing, and writing in unexplored regions of the Amazon River basin. He studied the languages and habits of the peoples he encountered; he collected butterflies, other insects, and birds; and he searched for clues to solve the mystery of the origin of plant and animal species. Except for one shipment of specimens sent to his agent in London, however, most of Wallace's collections were lost on his voyage home when his ship went up in flames and sank. Nevertheless, he managed to save some of his notes before his rescue, and from these he published several scientific articles, two books (
Palm Trees of the Amazon and Their Uses
and
Narrative of Travels on the Amazon and Rio Negro
, both 1853), and a map depicting the course of the Negro River. These won him acclaim from the Royal Geographical Society, which helped to fund his next collecting venture, in the Malay Archipelago.

Wallace spent eight years in the Malay Archipelago, from 1854 to 1862, traveling among the islands, collecting biological specimens for his own research and for sale, and writing scores of scientific articles on mostly zoological subjects. Among these were two extraordinary articles dealing with the origin of new species. The first of these, published in 1855, concluded with the assertion that “every species has come into existence coincident both in space and time with a pre-existing closely allied species.” Wallace then proposed that new species arise by the progression and continued divergence of varieties that outlive the parent species in the struggle for existence.

In early 1858 he sent a paper outlining these ideas to Darwin, who saw such a striking coincidence to his own theory that he consulted his closest colleagues, the geologist
Charles Lyell and the botanist Joseph Dalton Hooker. The three men decided to present two extracts of Darwin's previous writings, along with Wallace's paper, to the Linnean Society. The resulting set of papers, with both Darwin's and Wallace's names, was published as a single article entitled “On the Tendency of Species to Form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection” in the
Proceedings of the Linnean Society
in 1858. This compromise sought to avoid a conflict of priority interests and was reached without Wallace's knowledge. Wallace's research on the geographic distribution of animals among the islands of the Malay Archipelago provided crucial evidence for his evolutionary theories and led him to devise what soon became known as Wallace's Line, the boundary that separates the fauna of Australia from that of Asia.

Wallace returned to England in 1862 an established natural scientist and geographer. He published a highly successful narrative of his journey,
The Malay Archipelago: The Land of the Orang-Utan, and the Bird of Paradise
(1869), and wrote
Contributions to the Theory of Natural Selection
(1870). In the latter volume and in several articles from this period on human evolution and spiritualism, Wallace parted from the scientific naturalism of many of his friends and colleagues in claiming that natural selection could not account for the higher faculties of human beings.

Wallace's two-volume
Geographical Distribution of Animals
(1876) and
Island Life
(1880) became the standard authorities in zoogeography and island biogeography, synthesizing knowledge about the distribution and dispersal of living and extinct animals in an evolutionary framework. In addition to his major scientific works, Wallace actively pursued a variety of social and political interests. In writings and public appearances he opposed vaccination, eugenics, and vivisection while strongly supporting women's rights and land nationalization.

(b. June 26, 1824, Belfast, County Antrim, Ire. [now in Northern Ireland]—d. Dec. 17, 1907, Netherhall, near Largs, Ayrshire, Scot.)

S
cottish engineer, mathematician, and physicist William Thomson, also known as Baron Kelvin, profoundly influenced the scientific thought of his generation. Thomson, who was knighted and raised to the peerage in recognition of his work in engineering and physics, was foremost among the small group of British scientists who helped to lay the foundations of modern physics. His contributions to science included a major role in the development of the second law of thermodynamics; the absolute temperature scale (measured in kelvins); the dynamical theory of heat; the mathematical analysis of electricity and magnetism, including the basic ideas for the electromagnetic theory of light; the geophysical determination of the age of the Earth; and fundamental work in hydrodynamics. His theoretical work on submarine telegraphy and his inventions for use on submarine cables aided Britain in capturing a preeminent place in world communication during the 19th century.

Thomson's worldview was based in part on the belief that all phenomena that caused force—such as electricity, magnetism, and heat—were the result of invisible material in motion. This belief placed him in the forefront of those scientists who opposed the view that forces were produced by imponderable fluids. However, it also placed him in opposition to the positivistic outlook that proved to be a prelude to 20th-century quantum mechanics and relativity.