Biology

In 1876 Weismann brought forward his theory of heredity. This was a step in the doctrine of evolution. It denied the transmission of acquired characters, and did much to explain the process of heredity by the division of the parent cell. Whether or not we accept his thesis that acquired characters are never inherited, great credit is due him for his explanation of heredity. The principles of his theory are given below.

The most important step in biology in the last of the century is the development of the science of bacteriology. In 1849–50 Pollender and Devaine discovered minute bodies in animals that had died of anthrax. They called them bacteria, but did not yet consider them the cause of the disease. At this time the doctrine of spontaneous generation held full sway. Nobody dreamed of asking why wounds gangrened, grapes moulded, wine soured, or like seemingly foolish questions. But about 1857 Pasteur took up the study of fermentation and showed conclusively that its cause is the presence and growth of a micro-organism. Devaine in 1863 reinvestigated anthrax from this point of view and showed that such microbes were regularly present in the blood of animals that had died of the disease. In 1865 Pasteur showed that the way to prevent the silkworm disease, then ruining the industry in France, was to destroy everything infected with the microbe which caused the disease. In 1870 Koch of Wollstein took up the subject and invented his method of pure cultivation of the bacteria by cultivating them in a thin layer of jelly between glass plates, picking out species, and thus recultivating and selecting until the product was absolutely of one kind.

Pasteur and Cohn, by a series of the most careful experiments, conducted independently, gave the final blow to the spontaneous generation theory in the early seventies.

Pasteur began applying his method of inoculation about 1876. The first successful experiment was on animals inoculated with anthrax. The uninoculated died; the protected suffered no harm. Inoculation for chicken cholera was also successful. The germ has been found of tuberculosis (Koch, 1882), typhoid fever (Eberth, 1880), diphtheria (Klebs-Loeffier, 1883), cholera (Koch, 1884), lockjaw (Nicholaier, 1884), the grip (Canon, 1892), pneumonia (Frankel, 1886), etc. Pasteur’s treatment for hydrophobia, and Behring’s antitoxin give great hopes for the ultimate success of inoculation.