UBIQUITY OF BACTERIOPHAGE 417 



choose between these two hypotheses, for we have no direct proof of 

 either one, but the following experiment seems to favor the first of them, 

 although, as will appear, it by no means eliminates the second. 



I have a race of the bacteriophage, K (isolated from the feces of a 

 cholera convalescent) , which is very virulent for strain C of B. coli (isolated 

 from a case of cystitis) and for the dysentery organisms, Shiga, Flexner, 

 and Hiss. During the course of some studies made on a perfectly normal 

 individual I found that the stools contained a bacteriophage virulent 

 for strain V of B. coli (an old stock culture strain) . I had this individual 

 ingest 2 cc. of a suspension of bacteriophage K, and 36 hours later I 

 found that both races of the bacteriophage were present in his stools, — • 

 the race belonging to the individual himself, and race K. Specimens 

 collected 2, 3, and 4 days after the ingestion showed the same thing. 

 Those of the 5th, 6th, and 7th days showed only the race which 

 was present in the intestine before the ingestion. Race K had dis- 

 appeared. 



Similarly, we will see that when there exists in the intestine a culture 

 of a bacterium susceptible to the race of bacteriophage which is ingested, 

 the latter develops at the expense of these bacteria, but that it dis- 

 appears very soon after the bacteriophagy in vivo is completed. 



Whether the ingested bacteriophage corpuscles quickly lose their 

 characters in vivo, a change which does not occur in in vitro experiments 

 and which the observations made on the in vivo process renders im- 

 probable, or whether they are very quickly ehminated, the fact remains 

 that all of the bacteriophage corpuscles to be found in a filtrate from the 

 stool, either normal or pathological, belong to but a single race. 



The following fact, clearly demonstrated by Tomaselh^^** is of interest 

 in this connection. He showed that within the intestine of a given 

 individual a special race, always the same, persists. From an individual 

 who has had typhoid fever, even though the disease occurred several 

 years previously, he found that he could repeatedly recover from the 

 feces a race of the bacteriophage showing a virulence for B. typhosus, 

 a virulence which is but rarely demonstrated in the bacteriophage of 

 those who do not have the disease. This indicates a persistence, through- 

 out several years, of a single race, and this is hardly compatible with the 

 hypothesis that in vivo the races of the bacteriophage daily ingested 

 become uniform. 



The facts suggest, therefore, that in the intestine of each Uving being 

 there is a race of the bacteriophage possessing special characters, a race 

 which is in a sense pecuUar to the individual inasmuch as it possesses 

 its own different and variable virulences. 



