184 THE BACTERIOPHAGE AND ITS BEHAVIOR 



tubes were placed in the incubator at 41.5°C., the other 4 remained at 

 laboratory temperature. After 24 hours at 41,5°C., 7 of the 20 suspen- 

 sions were clear, 13 were cloudy. After 48 hours at this temperature all 

 20 of the suspensions were cloudy showing an abundant secondary cul- 

 ture. The four suspensions held at laboratory temperature were clear 

 and remained so for 2 months. 



A second part of this experiment, designed to show the effect of the 

 reaction of the medium was carried out at a temperature of 31°C. 



6. The bouillon used had a pH of 7.0. Bacteriophagy of all 24 tubes 

 was complete after 24 hours. After 48 hours the 24 tubes were turbid. 

 This, compared with part 5 above shows clearly the importance of the 

 hydrogen ion concentration. 



Experiments carried out with a potent Shiga-bacteriophage have given 

 results of the same nature ; the conditions of temperature and of reaction 

 exerting a comparable influence. 



It may be well to state, and later we will consider this point further, 

 that the optimum temperature may vary through some degrees. Fur- 

 thermore, we have seen that the optimum temperature is not the same 

 for all races; it is simply a question of adaptation as may be readily 

 demonstrated by experiment. But it is none the less true that insofar 

 as the bacteriophagy of B. dysenteriae and of the staphylococcus is 

 concerned, once an adaptation has been accompHshed, a temperature 

 of 32°C. is optimum — the critical temperature. Above this, whatever 

 may be the virulence of a bacteriophage and although it may be adapted 

 to induce bacteriophagy at a higher temperature, permanent sterility 

 of unfiltered suspensions of the bacteriophage is not uniformlij obtained. 



Experiment 5 (above) is of significance, for it shows that although 

 media in which bacteriophagy has been complete will remain sterile 

 indefinitely if conditions favorable to the bacteriophage are maintained, 

 they will yield secondary cultures if placed under conditions favorable 

 for the bacterium, although the media were perfectly clear and no 

 bacteria could be found even by examination of the sediment secured by 

 centrifugation. From where then, in these cases, are the resistant 

 bacteria derived? This is a question which we will consider in a later 

 section entitled Ultrabacteria. 



Macroscopic examination and biological reactions show that the tur- 

 bidity which occurs in bacteriophaged suspensions is due to the develop- 

 ment of bacteria of the same kind as those which formed the suspension 

 prior to bacteriophagy. These cultures which develop under these 

 circumstances, i.e., after bacteriophagy, I have termed secondary 

 cultures. ^^'''^^^ 



