THE MECHANISM OF BACTERIOPHAGY 119 



following liberations this interval of time becomes progressively greater, 

 and finally, the ruptures of the last cells of a series take place only 

 when the first burstings of the following series have conunenced. That 

 is, at this stage and under these circumstances the multipHcation of 

 the culture as a whole is in effect a continuous process. 



The phenomenon of bacteriophagy is biological in nature. There- 

 fore, it is impossible for its course to have the simplicity of a strictly 

 chemical reaction. 



Since the publication of my experiments upon this question many 

 students have studied the course of the multiplication of the bacterio- 

 phage. It also appears from the work of Maitland^^^ that the sudden 

 multiplication takes place only after an incubation period. I am not 

 able to insert here his experiments for he has adopted a method of 

 "titration" of the bacteriophage which does not allow of the exact 

 enumeration of the corpuscles. I shall return to this later, when 

 treating of the different methods proposed for measuring the activity 

 of the bacteriophage. Let it suffice here to say that from his experi- 

 ments it seems, as he has remarked, that at 37°C. there is no multipli- 

 cation during the first hour; sometimes during an even longer period. 

 Following this period of latency there is a period of rapid augmentation 

 occurring between the second and the third hours after the mixture 

 is made. During this increase the "titre" of the bacteriophage may 

 attain 10,000 times the original titre. The rate of the increase then 

 diminishes and the maximum concentration is reached at about the 

 fifth hour. 



These results agree, in a general way, with those which I have pub- 

 lished. But the great majority of those who have worked with the 

 bacteriophage have wished to generalize from their results and in this 

 tendency is to be found one of the causes of confusion in the study of 

 the bacteriophage. All that one may correctly conclude from a given 

 experiment is that under the conditions of this experiment such and 

 such a result has been obtained. Beyond this nothing is permissible. 

 Warranty for generalization is afforded only when a constant effect 

 is produced, whatever may be the race of the bacteriophage and what- 

 ever may be the bacterial species under investigation. 



Nevertheless, it may be stated that with a given bacterial species the 

 rapidity of fixation and consequently the rate of multiplication is a 

 function of the total 'Virulence," that is, an expression of the aver- 

 age virulence of the different corpuscles which are acting upon the 

 bacteria of the suspension. Each of the corpuscles present fixes itself 



