^94 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 their notable men. One of the most 



