PTOMAINES, LEUCOMAl'NES, AND BACTERIAL 

 PROTEIDS. 



INTRODUCTION. 



IT is customary to divide bacteria into the parasitic and 

 the saprophytic. The obligate parasite can live only on 

 living matter; the obligate saprophyte can live only on 

 dead i natter. Since all attempts to grow the bacilli of 

 syphilis and leprosy on artificial media have failed, they are 

 probably obligate parasites. True parasitic germs do not 

 prove speedily fatal to their hosts, because their continued 

 existence depends upon the continued existence of their host, 

 or on their transference to another host. Leaving out of 

 consideration the obligate bacterial parasites, about which 

 very little is known at best, the above classification becomes 

 of but little importance to us in a study of the causal rela- 

 tion of germs to disease, l>ecause a given bacterium may 

 grow and multiply in one part of the body, while it is 

 unable to do so in another ; or it may thrive in one species 

 of animal, while it finds the conditions unfavorable in an- 

 other species ; or similar differences may exist in individual 

 members of the same species. Thus, the white rat is ordi- 

 narily and naturally immune against the bacillus of anthrax, 

 lul if the rat be exhausted by being kept on a small tread- 

 mill for some hours it becomes susceptible to anthrax. 

 Recognizing these facts, we propose that bacteria be divided 

 into the toxieogenic and the non-toxicogenic. Since we 

 know of no infectious disease in which poisons are not 

 formed, the toxieogenic germs only are of interest to us. 



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