RESISTANCE OF BACTERIA 233 



If the hypothesis of Gildemeister were correct, that is to say, if all 

 bacterial strains contained a "lytic principle" it would only be necessary 

 to introduce a filtrate of any old culture of Shiga bacilli whatsoever 

 into a suspension of young bacilli in order to bring about bacteriophagy. 

 But this is not the case. Indeed, the fact that it is possible and easy to 

 purify any strain contaminated by the bacteriophage likewise renders 

 the hypothesis of Gildemeister inadmissible. 



It may not be out of place to mention the fact that the majority of 

 those who, at the beginning of their experiments upon the subject, 

 suggested that it was easy to isolate a bacteriophage from an old bac- 

 terial culture are not as emphatic on this point in their more recent 

 publications. Thus Otto and Munter^^^ now state that the nature of 

 the bacterial strain employed plays a role of the greatest importance. 

 This is to implicitly recognize that there are pure strains and that there 

 are contaminated strains. 



Immediately after the publications of Otto and of Weinberg appeared 

 I showed^^^ that in naturally mixed cultures the dissolving principle 

 represents an impurity in the bacteriological sense of this word, since 

 it is only necessary to carry out purifications upon an agar medium 

 according to the usual technic of colony isolation to obtain ultrapure 

 colonies cultivable indefinitely as such and from which it is henceforth 

 impossible to isolate a bacteriophage. This finding, since confirmed by 

 a number of workers, proves that the bacteriophage is foreign to the 

 bacterium inasmuch as a culture which contains it is divisible into two 

 fractions, the bacteriophage corpuscles on the one hand and the ultra- 

 pure bacteria on the other.* 



But are contaminated bacterial strains as common as some authors 

 assumed, especially at the beginning of their studies? The following 

 experiments afford an answer. 



Beckerich and Hauduroy^^ isolated, as I had done, a mixed culture of 

 bacteriophage and B. coli from a case of cystitis. They, also, succeeded 

 in purifying this contaminated strain by a single isolation, and from 

 that time on it was impossible for them to obtain from the ultrapure 

 strain a principle having an activity suggesting in any way the presence 

 of a bacteriophage. 



Tomaselli^^^ likewise encountered 5 cases of pyelocystitis yielding 

 mixed cultures of bacteriophage and B. coli. With the first 4 he readily 



* It seems, indeed, that a number of authors at the beginning of their studies 

 confused a simple temporary inhibition of growth with bacteriophagy. This 

 caused them to think that the bacteriophage was to be found everywhere. 



