PROPERTIES OF THE BACTERIOPHAGE 297 



took place when this filtrate was added to a suspension of susceptible 

 bacteria. These experiments have been criticized by Gildemeister and 

 Herzberg,235 by Prausnitz^^^ and by Flu.222 The last named author, 

 in particular, has investigated this method, finding that if a culture of 

 the staphylococcus is filtered through a very porous Berkefeld candle, 

 and if this candle is then treated according to the technic of Seiffert, 

 the temperature reached in the candle is insufficient to kill the staphylo- 

 cocci, although as is well-known the thermal death-point of this organ- 

 ism is about 60°C. This renders it all the more evident why the bac- 

 teriophage appeared to resist such high temperatures. 



One can only conclude from all of this that the bacteriophage corpuscle 

 is destroyed at a temperature which it is impossible to accui'ately deter- 

 mine, but which is certainly about 75°C. It is also obvious that the 

 "apparent" destruction corresponds to a complete attenuation of the 

 virulence, that this attenuation is progressive, and that it is proportion- 

 ate to the temperature to which the corpuscles are exposed. 



It is useless to cite figures for the different races, for whatever may be 

 the bacterial species attacked, inactivation of the bacteriophage takes 

 place, depending upon the virulence, at a temperature between 65 and 

 75°C. Only the figures given by Gerretsen, Gryns, Sack, and Sohn- 

 gen^^^ for their bacteriophage races virulent for B. radicicola will be 

 inserted here. This selection is made simply because their races are 

 active for an organism which is but very distantly related to all of the 

 other bacteria known to be susceptible up to the present time. They 

 found that one race of this bacteriophage, virulent for B. radicicola, 

 strain sarrandella, was inactivated at 65 °C., while the races virulent 

 for B. radicicola, strains clover and lupine, resisted this temperature. 

 Even with these newly discovered races, entirely unrelated to those 

 previously known insofar as the bacterium involved is concerned, we 

 find that the temperature of inactivation is essentially the same. 



From the experiments of de Necker^^^ it appears that not all of the 

 different corpuscles within a single suspension are inactivated at the 

 same temperature. Some of the corpuscles appear to be very fragile, 

 others more resistant. This is not at all surprising, for all bacterial 

 cultures show the same thing. It has long been known that when a 

 culture is exposed to heat a great many of the bacteria will die at a 

 temperature far below that requisite to render the entire culture sterile. 

 De Necker ''titrated" the bacteriophage by the method of dilutions, a 

 method which, in this case, is adequate, for here the differences are so 

 considerable that the lack of precision does not invalidate the results. 



