38o CLASSICS OF MODERN SCIENCE 

 bacteria than those intentionally introduced. It Is quite evident, from 

 a careful consideration of the two diseases produced in mice — 

 septicaemia and gangrene of the tissue — that I have succeeded in my 

 experiments in obtaining a pure cultivation. In the putrefying blood, 

 which was the cause of these two diseases, the most different forms of 

 bacteria were present, and yet only two of these found in the living 

 mouse the conditions necessary for their existence. All the others 

 died, and these two alone, a small bacillus and a chain-like micrococcus, 

 remained and grew. These could be transferred from one animal to 

 another as often as was desired, without suffering any alteration In 

 their characteristic form, in their specific physiological action and with- 

 out any other variety of bacteria at any time appearing. And fur- 

 ther, as I have demonstrated, it is quite in the power of the experi- 

 menter to separate these two forms of bacteria from each other. 

 When the blood in which only the bacilli are present is used, these 

 alone are transmitted, and thenceforth are obtained quite pure ; while 

 on the other hand, when a field mouse is inoculated with both forms of 

 bacteria, the bacilli disappear, and the micrococcus can be then culti- 

 vated pure. Doubtless an attempt to unite these two forms again in 

 the same animal by inoculation would have been successful. In short, 

 one has it completely In one's power to cultivate several varieties of 

 bacteria together, to separate them from each other, and eventually to 

 combine them again. Greater demands can hardly be made on a pure 

 cultivation, and I must therefore regard the successive transmission 

 of artificial Infective diseases as the best and surest method of pure 

 cultivation. And it can further claim the same power of demonstrat- 

 ing the existence of specific forms of bacteria, as must be conceded to 

 any faultless cultivation experiments. 



From the fact that the animal body is such an excellent apparatus 

 for pure cultivation, and that, as we have seen, when the experiments 

 are properly arranged and sufficient optical aids used, only one specific 

 form of bacterium can be found in each distinct case of artificial trau- 

 matic infective disease, we may now further conclude that when, in 

 examining a traumatic Infective disease, several different varieties of 

 bacteria are found, as e. g., chains of small granules, rods, and long, 

 oscillating threads — such as were seen together by Coze and Feltz in 

 the artificial septicaemia of rabbits — we have to do either with a com- 

 bined infective disease, — that Is, not a pure one, — or, what in the case 



