KOCH. 65 



the other a chain-like cocco-bacterium, were isolated, and after- 

 ward obtained entirely pure by culture on dry slides a plan 

 presently to be described. 



Why the field mice were insusceptible to the disease so 

 readily induced in the house mouse, remains a profound mys- 

 tery. Yet it is in accord with facts that are continually 

 coming to light. It is a well-known fact that certain persons 

 resist the contagium of smallpox, while others around them 

 are struck down; and the same is true of every other con- 

 ta'nous disease. It is also a well-known fact that some 



o 



classes of animals are insusceptible to certain diseases common 

 to other animals nearly related to them. It would seem that 

 the organism inducing the particular disease does not find in 

 this or that animal a suitable habitat, but why, is unknown. 



As I have said, this class of experiments had been made by 

 many before Dr. Koch ; but he had developed a distinctive 

 feature. He had demonstrated that the same tissues or fluids 

 might contain germs, which, when separated, would produce 

 separate and distinct processes of disease. Heretofore, as has 

 been said, this class of experiments had only succeeded in pro- 

 ducing septicaBmia and pyaemia, which were regarded as parts 

 of the same process. And this result was induced, no matter 

 what the disease with which the patient from whom the 

 material was obtained, may have died ; results very confusing 

 to those who believed that different diseases are induced by 

 distinct and separate germs. 



We have already spoken of the fact that these results were 

 very nearly identical with ordinary blood poisoning from 

 wounds. Now in the discussion of Dr. Koch's experiments 

 a new thought was developed. The substances injected were 

 all contaminated with septic germs ; and these virulent germs 

 had killed the animals experimented upon, before other and 

 slower acting germs had time to produce their results. The 



