BACTERIOPHAGT IN A FLUID MEDIUM 61 



After 6 hours the turbidity was the same as at the beginning. Bac- 

 teriophagy had not taken place. But the bacteriophage was not 

 destroyed, for a drop of this suspension spread upon agar failed to yield 

 a growth after incubation. Nor were the bacilli killed, for the inocula- 

 tion of a drop of the control suspension, uninoculated with the bacterio- 

 phage, yielded a growth of B. coli. 



These experiments, therefore, justify the conclusion that under the 

 conditions under which they were performed bacteriophagy is effected 

 up to temperatures of 46°C., and that at this temperature it is very 

 rapid indeed, even more rapid than at 37°C. 



It is difficult to explain the results obtained by Doerr and Griininger. 

 But one possibihty suggests itseK, namely, that their results were due 

 to the unintentional use of an acid bouillon as culture medium, or, which 

 would amount to the same thing, to the use of a medium containing 

 sugar and rendered acid by the fermentation caused by the colon 

 bacilli. This possibility is suggested to explain the destruction of the 

 bacteriophage at this temperature. As for the absence of bacteri- 

 ophagy at this temperature (43°C.) it is readily explained by the fact 

 that the temperature limit varies with the race of bacteriophage em- 

 ployed. For example, in so far as B. coli is concerned, using the same 

 strain as that which was employed in the experiments previously cited, 

 but using a bacteriophage of a different race (isolated from the feces 

 of a convalescent from typhoid fever) the dissolution of the bacilli 

 was not complete at 42°; at 43° it did not take place at all. 



In bacteriophagy it is vain to undertake to estabhsh rigid rules 

 (there are some who even speak of "laws") fixing with an air of finality 

 the conditions of the phenomenon. What is true for one race of the 

 bacteriophage is not necessarily true for another. 'T have isolated 

 several hundred strains of this bactericidal "principle," and I have 

 not yet found two which were absolutely identical." These words 

 appeared in one of my first publications,^'^^ and it is indeed unfortunate 

 that those who have since worked with the phenomenon have been 

 unable to comprehend their true meaning, since had they done so 

 they would have refrained from stating many "rules" which further 

 investigation has not confirmed. 



The single method to follow, — indeed, the sole logical procedure if 

 one wishes to determine as exactly as possible any one of the conditions 

 of bacteriophagy, — is to execute a large number of experiments, utiliz- 

 ing different bacterial species and even different strains of the same 

 species, combining each one of them with several races of the bacterio- 



