RESISTANCE OF BACTERIA 



189 



The contents of a tube that gave a secondary culture is filtered 

 through infusorial earth and a bougie. Twelve tubes of a Shiga 

 suspension are inoculated, each receiving 0.001 cc. of the filtrate. Per- 

 fect dissolution is seen in all tubes, and in all but one the dissolution is 

 permanent. This single tube again becomes turbid after 4 days. 



From this it is clear that the bacteriophage has not lost in virulence, 

 and that secondary cultures can not be ascribed to a change in that 

 direction. The bacteriophage remains virulent, coexisting with bacteria 

 which have become resistant. The secondary cultures, then, are the 

 result of an adaptation undergone by the bacterium which acquires an 

 immunity to its parasite. 



It has already been shown that the number of corpuscles inoculated 

 is without influence on the appearance of secondary cultures. The 



conflict is not one of numbers; it is rather a struggle in which the signifi- 

 cant factors are virulence on one side and ability to resist on the other. 



A suspension of B. dysenteriae, 250,000,000 per cubic centimeter, is 

 distributed into 6 tubes and these are inoculated with variable quanti- 

 ties of the same bacteriophage filtrate. The results obtained are given 

 in table 16. 



The tubes yielding secondary cultures are distributed at random 

 throughout the series, showing no fixed relationship to those tubes in 

 which the dissolution was permanent. 



Another experiment may be presented, indicating as it does, the ran- 

 dom manner in which secondary cultures may develop. 



This experiment shows the serial activity of the bacteriophage 

 together with the appearance of secondary cultures. Each tube of the 

 series is prepared with a suspension of B. dysenteriae, 250,000,000 

 per cubic centimeter, and into each is introduced 0.001 cc. of the dis- 



