BACTERIOPHAGY IN A FLUID MEDIUM 63 



Several of my laboratory strains of B. pestis have an optimum 

 growth temperature of 32 to 33°C. Two races of the bacteriophage 

 acted upon these cultures most vigorously at temperatures of 37 to 

 38°C. 



With B. coli, we have seen that, at least with certain races of the 

 bacteriophage, an extremely rapid dissolution occurs at a temperature 

 of 46°C., under conditions where the development of the colon bacilli 

 did not take place, or at least where it was so slow that it could not be 

 detected in control suspensions not containing the bacteriophage. 



Pressure conditions 



According to experiments which I have carried out with B. dysen- 

 teriae, it would appear that bacteriophagy occurs as actively in vacuo 

 as under normal atmospheric pressure. ''^^ Various authors, Wollstein 

 in particular, have reached this same conclusion. 



Viscosity of the medium 



j)QgPj.i78 jjg^g stated that in a bouillon medium the addition of an 

 adequate amount of gelatin prevents dissolution of the bacteria by 

 the bacteriophage. The experiment upon which he based this con- 

 clusion was performed with B. coli. In collaboration with Berger,^^' 

 Doerr reconsiders this statement, modifying considerably the rigor 

 of his first conclusions. He observes that it is necessary that the 

 medium contain a certain quantity of gelatin in order to prevent the 

 dissolution of the bacteria, and that the dissolution is the less as the 

 concentration of the gelatin is increased. Agar acts in the same way. 

 On the other hand, the greater the concentration of the bacteriophage 

 present, the higher must be the content in gelatin to prevent the dis- 

 solution. But despite this inhibitory effect the bacteriophage is still 

 capable of acting upon the bacteria even in media with very high 

 concentrations of gelatin, for, as he showed, the principle reproduced in 

 such a medium. Consequently bacteriophagy must have taken place. 



In a series of independent investigations Nakamura has studied the 

 effect of substances having properties analogous to those of gela- 

 tin4fi8,469 jjg showed that gum tragacanth, or salep, exerted an in- 

 fluence upon bacteriophagy comparable to that of gelatin. The 

 sugars also, but to a less degree, interfered with the process. It is 

 significant that he observed that all races of the bacteriophage do not 

 behave in the same way. With some the activity is but slightly modi- 



