THE MECHANISM OF BACTERIOPHAGY 117 



After 4| hours, the counts are 145 and 160 (average, 152), indicating 

 that the suspension contains 75,000; a number but shghtly higher than 

 the count after 4 hours. 



After 5 hours the agar tubes remain sterile. "When diluted to 1 : 1000 

 in a suspension of Shiga bacilh and transferred immediately to agar 

 in the same way, the tubes give 4 and 6 plaques. Thus, it appears 

 that after 5 hours the suspension contains about 1,500,000 bacterio- 

 phage corpuscles per cubic centimeter. 



Although all authors are virtually in agreement with me upon the 

 question of the specific fixation of the bacteriophage to the bacteria, 

 several have denied that the multiplication occurs through successive 

 sudden increments. Thus, Doerr found that the increase in "lytic 

 substance" was very rapid but took place gradually, the titre increas- 

 ing by about 10 times every 15 minutes. After having carried out 

 many tests upon a variety of bacteria with different races of the bac- 

 teriophage I adhere definitely to my previous statement,^-^ namely, 

 that the increase in the number of corpuscles does not take place in a 

 continuous progressive fashion, but by successive liberations. It may 

 be pertinent to observe that in order to clearly observe this phenom- 

 enon it is essential that the experiments be performed in such a way 

 that the course of the reaction is not obscured. To effectively demon- 

 strate the phenomenon it is necessary to observe the following condi- 

 tions: (1) To work with a bacterial species which undergoes a rapid 

 bacteriophagy. Such a one is the Shiga bacillus. (2) To work with 

 a bacteriophage of maximum activity for the bacterium in question. 

 (3) To utilize a very small number of bacteriophage corpuscles, acting 

 upon a large number of bacteria. 



The reasons which make these conditions essential if the phenomenon 

 is to be observed distinctly can readily be understood. If one uses a 

 bacteriophage of weak activity the corpuscles of the successive genera- 

 tions become fixed very slowly and at a very unequal rate. Those 

 fixed at first have already formed a colony and have caused the rupture 

 of the bacterium before the other corpuscles are even fixed. Under 

 such circumstances it can be understood that it is impossible to observe 

 the true course of multiplication of each corpuscle, and Doerr is then 

 apparently correct, for the total course of the multiplication is indeed 

 progressively continuous. 



Even in the case of a bacteriophage of maximum activity the fixation 

 of all of the corpuscles does not take place with mathematical precision 

 within the same interval of time. Obviously, for this there are several 



