204 BIOLOGY AND ITS MAKERS 
disease, we come, then, first to the year 1837, when the 
Italian Bassi investigated the disease of silkworms, and 
showed that the transmission of that disease was the result 
of the passing of minute glittering particles from the sick to 
the healthy. Upon the basis of Bassi’s observation, the 
distinguished anatomist Henle, in 1840, expounded the 
theory that all contagious diseases are due to microscopic 
germs. 
The matter, however, did not receive experimental proof 
until 1877, when Pasteur and Robert Koch showed the direct 
connection between certain microscopic filaments and the 
disease of splenic fever, which attacks sheep and other cattle. 
Koch was able to get some of these minute filaments under 
the microscope, and to trace upon a warm stage the different 
steps in their germination. He saw the spores bud and 
produce filamentous forms. He was able to cultivate these 
upon a nutrient substance, gelatin, and in this way to obtain 
a pure culture of the organism, which is designated under 
the term anthrax. He inoculated mice with the pure culture 
of anthrax germs, and produced splenic fever in the inocu- 
lated forms. He was able to do this through several genera- 
tions of mice. In the same year Pasteur showed a similar 
connection between splenic fever and the anthrax. 
This demonstration of the actual connection between 
anthrax and splenic fever formed the first secure foundation 
of the germ-theory of disease, and this department of inves- 
tigation became an important one in general biology. The 
pioneer workers who reached the highest position in the de- 
velopment of this knowledge are Pasteur, Koch, and Lister. 
Veneration of Pasteur.—Pasteur is one of the most con- 
spicuous figures of the nineteenth century. The veneration 
in which he is held by the French people is shown in the 
result of a popular vote, taken in 1907, by which he was 
placed at the head of all theirnotable men. One of the most 
