THE MECHANISM OF BACTERIOPHAGY 107 



different experiments is the time requisite for the fixation, and this 

 varies with the bacterial species and with the race of the bacteriophage, 

 as well as with the reaction of the medium, the temperature, and other 

 environmental conditions. 



With a single strain of bacteria the fixation is the more rapid and 

 complete the more active the bacteriophage. It is particularly perti- 

 nent in this connection to remember that the mechanism of bacteri- 

 ophagy can be studied only with races of the bacteriophage of maximum 

 activity. With races of less potency the phenomenon of bacterial 

 resistance masks to a greater or less degree the processes of attack. 



By a series of experiments performed with different bacterial species 

 I' am convinced that with bacteriophage races of low potency it is 

 impossible to demonstrate the process of fixation to the bacteria. 

 At least, it is impossible to demonstrate that the corpuscles disappear 

 from the liquid. The reason for this is obvious, for with such 

 races fixation takes place slowly and instead of the process occur- 

 ring almost simultaneously with practically the entire number of inocu- 

 lated corpuscles, as is the case when the bacteriophage is very active, 

 the time of fixation varies enormously among the different corpuscles. 

 It thus happens that a great number have not been fixed when those 

 which are first fixed have already commenced to reproduce. Conse- 

 quently, the fixation remains undetected. 



Carrying out experiments analogous to those which I have described 

 but employing filtration instead of centrifugation, Janzen and Wolff^" 

 obtained the following results in two experiments with B. typhosus 

 using different races of the Typhoid-bacteriophage. 



Number of free corpuscles per cubic centimeter, unfixed to the bacteria 



I. Immediately after inoculation 18,000,000 



After 15 minutes 280,000 



II. Immediately after inoculation 30,000,000 



After ISminutes 4,000,000 



It is probable that the number of bacteriophage corpuscles fixed 

 would have been still greater if the counts had been made some 5 or 

 10 minutes later. 



The process of fixation is lacking when a bacteriophage is placed in 

 contact with a bacterium insusceptible to bacteriophagy by the partic- 

 ular bacteriophage involved.^^i ^i^h but one exception all of those 

 who have studied this question agree on this point. Later we will 



