166 THE BACTERIOPHAGE AND ITS BEHAVIOR 



actually destroyed or attenuated to such an extent that its presence 

 can no longer be detected. In all these instances the bacteriophage 

 shows a recuperative power, the virulence being restored when the tem- 

 perature to which the corpuscles have been subjected is not higher than 

 72°C. 



Anti-staphylococcus hacteriophage 



Attenuation of this bacteriophage is already manifest after heating 

 to 60°G. Sul^cultures of suspensions which have not been dissolved 

 show that it is a simple attenuation, for, even with suspensions inocu- 

 lated with a bacteriophage previously held at 72°C. for thirty minutes, 

 plaques are obtained characteristic of the presence of an active bac- 

 teriophage. Moreover, two passages suffice to restore the original viru- 

 lence to corpuscles heated to 62, 64, 66, and 68°C. After heating at 70 

 and 72°C. the attenuation of virulence does not disappear until after 

 six passages. When heated to 75°C. the bacteriophage is deprived of 

 all activity. 



It may be concluded from these experiments that all races of the 

 bacteriophage react to temperature in the same manner. When heated 

 above 60°C. they are attenuated more or less rapidly, the speed de- 

 pending to some extent upon the bacterial species for which they are 

 active. But all are completely killed, or at least paralyzed, at a tem- 

 perature of about 75°C. 



The results observed in these experiments can not be ascribed to a 

 reduction in the number of corpuscles, for the Shiga-bacteriophage used, 

 like the Staphylo-bacteriophage, had caused complete bacteriophagy 

 in a unit volume before exposure to the high temperature, and it will 

 do the same after the vu'ulence is again increased. 



My experiments have also shown that bacteriophage races of low 

 virulence are attenuated at lower temperatures than are races possessing 

 a more outspoken virulence for the same bacterial strain. 



Time also exerts an effect upon virulence, but here there is a very great 

 difference in the effects, depending upon the race of bacteriophage, and 

 especially upon its virulence. Bacteriophage races possessing a high 

 virulence are in general but shghtly modified while those of low virulence 

 are much more sensitive. 



Asheshov^* was the first to observe that certain races of the bacterio- 

 phage may lose their virulence very rapidly. A Flexner-bacteriophage 

 which I isolated, and which had a relatively high virulence, manifested 

 a very considerable attenuation even within a period of two months, 



