292 THE BACTERIOPHAGE AND ITS BEHAVIOR 



plaques of the bacteriophage on agar, or suspensions contained in quartz 

 tubes, to a Heraeus lamp operating under 4 amperes at 220 volts. 



Although under these conditions, B. radicicola was killed after 

 exposure for 15 minutes, the bacteriophage was intact after 30 minutes. 

 Indeed, it was still alive after 2 hours, but was completely destroyed 

 after 2| hours. 



Brutsaert^°^ has investigated the effect of radium emanations. In his 

 experiments the radio-active energy, measured as 7 rays, was equivalent 

 to 0.914 gr. of radium. He found that after a prolonged exposure, 

 the bacteriophage remained intact. A Coli-bacteriophage, of average 

 virulence, was but slightly attenuated after an exposure of 24 hours, 

 for its virulence was fully restored by a single passage. 



The effects of irradiation may be summarized briefly by stating that 

 the bacteriophage behaves in essentially the same way as does the 

 bacterium. 



6. EFFECT OP TEMPERATURE 



Among the very first of my reports on bacteriophagy and the bac- 

 teriophage itself there appeared the statement^^^ that the Shiga-bacterio- 

 phage resisted a temperature of 65°C. when exposed for a half-hour. 

 Kabeshima^^^ reported it was not destroyed at 70°C., but that destruc- 

 tion occurred only when it was heated for a half hour at 75°C. Kutt- 

 ijgj.398 made the same observation in determinations with the Typho- 

 bacteriophage. 



In collaboration with Pozerski^''*' additional consideration was given 

 to this question of heat-resistance and from these studies the reason 

 for the divergent reports became apparent. It was found that the 

 destruction of the corpuscles is preceded by an attenuation in the 

 virulence, the attenuation being the more pronounced as the tempera- 

 ture to which the corpuscles are heated is increased. For all corpuscles, 

 of whatever virulence and of whatever race the temperature of apparent 

 destruction, that is to say, of complete inactivation* is about 75°C. 

 The following experiments demonstrate this. 



A bacteriophage suspension, previously filtered through a candle, 

 is taken up in a series of capillary pipettes, and the pipettes are care- 

 fully sealed at both ends. The pipettes are then completely immersed 



* I repeat that we can only recognize the bacteriophage through its virulence. 

 Loss of virulence or destruction of the corpuscle as such would lead to the same 

 phenomenon, — absence of bacteriophagy. After exposure to 75°C. the bacterio- 

 phage is completely avirulent. It may not be destroyed until the temperature 

 reaches 80 or 90°C., but this we can not determine. 



