294 THE BACTERIOPHAGE AND ITS BEHAVIOR 



tected. In all instances where a complete destruction does not take 

 place, the corpuscles manifest a recuperative power, the virulence 

 being restored more or less readily by subsequent passages if the tem- 

 perature to which they have been subjected is not higher than 72°C. 



Staphylo-haderiophage 



This race of the bacteriophage appears to be somewhat more sensitive 

 than are many races, for after exposure to a temperature no higher than 

 60°C. it would appear that some attenuation occurred. Subcultures 

 from those tubes which failed to show a dissolution clearly demonstrate 

 that the changed activity is referable to a simple attenuation, for even 

 those suspensions inoculated with a bacteriophage previously heated 

 for 30 minutes at 72°C. gave plaques characteristic of an active bac- 

 teriophage. Here again, the original virulence may be restored to sus- 

 pensions heated at 62, 64, 66 and 68°C. by two passages. With suspen- 

 sions heated to 70 and 72° six passages were required to bring back the 

 virulence. A temperature of 75°C. deprived the bacteriophage of all 

 activity. From these experiments it might be concluded that all races 

 of the bacteriophage react in the same manner to the influence of 

 temperature. As a matter of fact with each individual race the attenu- 

 ation begins at a given temperature, varying with the race, but as to the 

 upper limit, all races are permanently destroyed, or at least rendered 

 completely avirulent, at temperatures approximating 75°C. (d'Herelle 

 and Pozerski^^"). 



It appears clearly from these experiments that attenuation through 

 heat begins to occur at a temperature rather more than 10° below 

 the point where the activity becomes definitely lost. They show like- 

 wise that it is unsafe to conclude that the bacteriophage is destroyed 

 simply because it ceases to provoke bacteriophagy. It is always 

 necessary to prove the question of destruction by making a few passages 

 at the expense of a susceptible bacterium, for if the attenuation has not 

 been extreme the virulence may be enhanced again. 



Otto, Munter and Winkler,^^'' as well as Hauduroy,^*^ have shown 

 that the attenuating effects of temperature occur the more readily as 

 the virulence is less strong. That such a relationship should obtaia is 

 obvious, for since the virulence becomes gradually and progressively 

 attenuated as the temperature is raised it is clear that when the initial 

 virulence is weak the race will reach the point of complete attenuation 

 more quickly. 



Otto, Munter and Winkler^^^ have shown also that with a single race 



