86 BACTERIOLOGY. 



ditions will not produce disease. As already men- 

 tioned, bacteria even under similar conditions differ 

 enormously in the amount of poison which each organ- 

 ism produces and in their ability after gaining entrance 

 to multiply in the body. 



To understands all the production of disease through 

 bacteria we must recognize that both the body invaded 

 and the bacteria which invade are living organisms. 

 They are in bulk, wide apart, but both have life. Just 

 as there are different races and species of animals, there 

 are different races and species among bacteria, and just 

 as the descendants of one animal species under changing 

 conditions gradually become diverse, so do the descend- 

 ants of one bacterial species. Considering these facts, 

 we can readily understand how all of bacteria do not 

 grow equally well in every variety of animal, nor even 

 find the body of the same animal always equally suit- 

 able. This is all the more apparent when we consider 

 that the study of bacteria in the more simple and 

 known conditions of artificial culture media has already 

 shown us how extremely sensitive many bacteria are to 

 slight chemical, thermal, and other changes. 



Thus if we take specimens of diphtheria bacilli from 

 three different cases of diphtheria, we find that on grow- 

 ing them for several days in suitable bouillon one will 

 have produced poison in the culture fluid to such a 

 degree that one drop suffices to kill a large guinea- 

 pig; the second, grown in a similar manner, will kill 

 another animal of the same size with half a drop; 

 while the third will kill with one-tenth of a drop. 

 In other words, different varieties of diphtheria bacilli 

 under similar conditions have different toxin-producing 

 powers. 



