RESISTANCE OF BACTERIA 223 



tion may occur and that the formation of a mucous capsule may become 

 a permanent characteristic, as is indicated by the experiments of Bordet 

 and Ciuca, and by those of Gratia, who have obtained ultrapure strains 

 of B. coli cultivable indefinitely as B. aerogenes. 



But here is another experiment which tends to show that under the 

 action of bacteriophage a mutation of another type may occur. 



Flu^^^ has kept in his stock cultures a bacillus (KB) isolated from a 

 patient with sprue. This bacillus presents all of the characters of a 

 Flexner dysentery organism, except in the matter of its agglutinability 

 with anti-Flexner sera. That it is actually an inagglutinable Flexner 

 bacillus is shown by its absorption of the corresponding agglutinins, 

 by the fixation reaction, and by its agglutinogenic character. A serum 

 prepared with this organism agglutinated different strains of B.dysen- 

 teriae Flexner in a dilution of 1 : 7000 but the serum remained inert upon 

 the KB bacillus itself. 



Flu then found that this bacillus is completely refractory to the action 

 of a Flexner-bacteriophage although the Flexner dysentery bacilli are a 

 homogeneous species, and although the races of the bacteriophage 

 against which the KB bacillus proved to be refractory, caused, neverthe- 

 less, bacteriophagy with various normal strains among the cultures of 

 Flu.* 



Here is, then, an abnormal strain of the Flexner bacillus (a species 

 which is homogeneous), endowed with the refractory state toward the 

 bacteriophage and this refractory state is due to the fact that the proto- 

 plasm of this bacterium destroys bacteriophage corpuscles. It has, 

 then, a true immunity. It is very probable that this refractory state 

 was acquired! in the body of the patient. Ordinarily in the absence of 

 virulent bacteriophage corpuscles the refractoiy state is gradually lost. 

 In the case of bacillus "KB" it appears that a fixed mutation has 

 occurred, the refractory state being permanent in the absence of the 

 bacteriophage. If the fact of such a mutation, here probable, but 

 obviously subject to discussion, were experimentally demonstrable 

 beyond all possible doubt, it would be of considerable importance in 



* This is the bacillus "KB" of which we have already spoken with regard to 

 destruction of the bacteriophage corpuscles in the bacterial protoplasm. Flu 

 has been able to show that this refractory bacillus "phagocytizes" the corpuscles. 



t I have isolated from a patient a Flexner bacillus which was refractory to the 

 bacteriophage and inagglutinable, but in this case the refractory state gradually 

 diminished during cultivation in the absence of the bacteriophage. 



