THE CAUSE OF INFECTIOUS DISEASE. 261 



when they adapt themselves to the conditions 

 of intestinal putrefaction. They may for the 

 same reason invade the living organism when- 

 ever its normal protecting power has become 

 enfeebled through errors in l^giene. 



The second question is, Do the so-called 

 " specific " disease germs vary in their capacity 

 to produce disease ? Buchner was the first to 

 succeed, upon the basis of systematic experi- 

 ments, in proving that the so-called anthrax 

 bacilli can be modified artificially in such a way 

 that they are no longer able to bring about any 

 illness, but behave like perfectly harmless 

 saprophytes. The same discovery was soon 

 afterwards made accidentally by Pasteur in re- 

 gard to the bacteria of the disease called chicken 

 cholera, and we now know from hundreds of 

 experiments that no peculiarity of disease-pro- 

 ducing bacteria is more easily affected than the 

 very capacity in question, commonly presumed 

 to be " specific," namely that of producing dis- 

 ease. The physician who seeks the " essence " 

 of the disease in the " specificity " of the disease 

 germs can plainly attach importance only to 

 those parasites whose " specific " capacity of 

 producing disease is invariably exercised. 

 The facts that demonstrate the variability of 

 this capacity therefore obviate all need for seek- 

 ing an "essence." 



