RESISTANCE OF BACTERIA 195 



sion is inoculated with a trace of a very active race of the bacteriophage, 

 and finally, the active bacteriophage reappears after a series of subcul- 

 tures on agar in the course of which all the bacillary cultures have been 

 normal. This corpuscle can only be one of those which had disappeared. 

 The fact, demonstrated by experiment, of the penetration of virulent 

 bacteriophage corpuscles into the bacteria, warrants us in thinking that 

 this corpuscle (but slightly virulent) has been preserved in a latent 

 living state within the interior of the bacterium. At a given moment 

 the resistance of the bacterium is broken down and infection results 

 (d'Herelle'^^i), 



The fact that a bacteriophage corpuscle may penetrate a bacterium 

 and be destroyed there has been confirmed by Flu-^^ w^ho has carried 

 out the following admirable experiment. 



Flu found, among the cultures of the Institute of Tropical Medicine 

 at the University of Leiden, a bacterium (isolated from the stools of an 

 individual affected with sprue) which presented all of the cultural, 

 biochemical, and serological characteristics of B. dysenteriae Flexner, 

 except that it was inagglutinable. This bacillus was refractory to all 

 races of bacteriophage virulent for B. dysenteriae Flexner. Neverthe- 

 less, suspensions of this bacillus, whether living or killed by heat, fixed 

 the bacteriophage corpuscles of these races. 



By a method of grinding with anhydrous sodium sulphate, a method 

 which will be described in a later section, Flu was able to recover the 

 corpuscles which had been fixed to the killed bacteria. When they 

 had been fixed to living bacilli he was unable to recover them. As he 

 has observed, this fact can only be explained by a destruction of the 

 bacteriophage corpuscles by the protoplasm of the bacillus. 



I have since proved by this same method that a bacterium rendered 

 experimentally refractory behaves in the same manner. As a matter of 

 fact, this experiment was carried out with the refractory strain of 

 staphylococcus V, mentioned in a preceding paragraph. Destruction 

 of the bacteriophage occurred not only with the corpuscles of race v, 

 but also with those of race h. The destruction was, as a ruk;, complete 

 when the number of corpuscles in proportion to the number of cocci was 

 not too great, for example, when there was not more than 1 corpuscle to 

 100 cocci. When the ratio was higher very frequently unfixed corpus- 

 cles remained. 



A bacterium possessing a moderate degree of resistance may destroy 

 bacteriophage corpuscles of low virulence. A refractory bacterium may 

 destroy corpuscles of maximum virulence. 



