168 MICRO-ORGANISMS AND DISEASE. [CH. xvn. 



are pathogenic while others are quite harmless. The latter 

 remain so no matter under what conditions and for how long 

 they grow. 



I have made a series of experiments with the view to obtain 

 pure cultivations of definite septic micro-organisms : various 

 species of micrococci, bacterium termo, and bacillus subtilis, 

 of which the morphological characters could with precision be 

 ascertained and which at starting were tested to be barren of 

 any power of inducing disease. I have cultivated these in pure 

 cultivations for many generations, and under varying conditions, 

 and then I have inoculated with them a large number of 

 animals (mice, rabbits, and guinea-pigs) ; and to put it briefly, 

 I have not found that hereby any of them acquired the leas* 

 pathogenic power. 



