NATURE OF BACTERIOPHAGE 



345 



ninth passage it caused an almost complete dissolution of bacteria in 

 glucose bouillon. The results of the twelfth passage are given in 

 table 34. 



It is obvious [states this author] that after 12 passages the bacteriophage has 

 become adapted to the harmful action of the medium and of the acid in statu 

 nascendi. The final development (after 24 hours) of bacilli in the glucose bouillon 

 must be attributed to the presence of bacteriophage-resistant bacteria, which 

 have within this interval of time, so acidified the medium that even this race of 

 acid-tolerant bacteriophage is unable to attack them. 



It may be observed, however, that the activity of the bacteriophage weakens, 

 although very slowly, during the course of passages through an acid medium. 

 The number of bacteriophage corpuscles per cubic centimeter at the end of the 

 experiment was comparatively smaller, just as the virulence was lower. 



From this is appears that the bacteriophage although losing somewhat 

 in virulence, may become accustomed to the harmful action of acids. 



Some of my experiments have shown the same thing, and that not only 

 is the virulence of the bacteriophage attenuated by growth in an acid 

 medium, but also by cultivation at a high temperature. And, as stated 

 above, Gildemeister has shown that cultivation at a low temperature also 

 results in a diminished virulence. The same thing occurs with patho- 

 genic bacteria; they can be adapted to grow in an unfavorable medium, 

 but their virulence suffers. 



This is a fact worthy of note : Adaptation to a harmful action, instead 

 of leading to a corresponding increase in virulence, is accompanied by an 

 attenuation. 



Schuurman"^ attempted to adapt a Flexner-bacteriophage, which 

 showed a maximum degree of virulence in a medium with a pH of 8.2, 

 to effect bacteriophagy in media of increasing degrees of acidity, the 

 tubes in which the contacts were made being held at a temperature of 

 37°C. At the twenty-second passage he obtained a complete dissolu- 



