BACTERIOPHAGOUS ANTISERUM 141 



It retains for a long time its hereditary faculty of attacking the 

 organisms of the colon-typhoid-dysentery group, even if it is 

 cultivated for many generations at the expense of another bac- 

 terial species. 



INCIDENTAL CONDITIONS RESULTING FROM THE EXISTENCE OF 

 THE BACTERIOPHAGE 



I wish to note certain incidental consequences which spring 

 from the facts which we have considered. Although accessory, 

 these consequences are of some practical significance and it may 

 be well to mention them. 



Because of the ubiquity of the bacteriophage and its con- 

 stant presence in all living beings, and because of the resistance 

 which the bacteria are able to oppose to its action, and which gives 

 birth to the phenomenon of mixed cultures, it is henceforth 

 necessary to verify the purity of bacterial cultures from the 

 point of view of possible contamination not only by another 

 bacterial species, but also by an ultramicrobe. 



We will see, for example, that in B. coli pyelonephritis, the 

 pathogenic agent is always a colon bacillus which is resistant to 

 the bacteriophage. If one plants the urine from a case of pyelone- 

 phritis on agar for the purpose of isolating the etiological agent 

 one is always liable to find mixed colonies of the colon bacillus 

 and the bacteriophage. Subculture from these mixed colonies 

 will give mixed cultures, indefinitely cultivable in this form. 

 Such cultures are usually considered pure, for they contain no 

 other organism visible under the microscope. They are, how- 

 ever, contaminated by the bacteriophagous ultramicrobe; they 

 are not "ultrapure," and investigations undertaken with such 

 mixed colon-bacteriophage cultures may furnish peculiar results, 

 especially if they are used in immunological experimentation. 

 It is not to be assumed that I have mentioned an exceptional 

 case, far from it, as the two following examples demonstrate. 



In two different instances, both accidental findings, I have 

 demonstrated that cultures of the colon bacillus isolated origi- 

 nally from cases of cystitis in the hospital, were in reality mixed 

 cultures. In both instances it was easy to isolate from these 

 cultures a very active bacteriophage. 



