BACTERIA SUSCEPTIBLE TO BACTERIOPHAGY 



251 



have confirmed this observation Reichert,^^" who has especially studied 

 this question, may be mentioned. This author has found, indeed, that 

 the opposite effect may also take place, namely, that through passages 

 at the expense of one strain a virulence for another strain may be lost. 



Typhoid bacilli which have acquired a resistance are inagglutinable 

 or but slightly agglutinable by an antiserum.* They kill laboratory 

 animals in smaller doses than do normal bacilli. f 



The virulence of a bacteriophage is rarely limited to B. typhosus, 

 but usually extends to one or several related species. This is, indeed, 

 a rather general phenomenon and it will be unnecessary to repeat this 

 comment in connection with each bacterial species considered. A 

 bacteriophage is rarely virulent for but a single bacterial species. 



Occasionally it is possible to isolate from the intestines of normal 

 men and of animals virulent races of the bacteriophage but as a rule, 

 when derived from these sources the virulence is weak. On the con- 



trary the virulence is very high in races derived from the stools of 

 typhoid convalescents and it was from such a source, that is, a con- 

 valescent from an acute infectious intestinal disease, that it was first 

 isolated (d'Herelle^^^). Races may also be found in the urine of con- 

 valescents (d'Herelle^'i"), and are constantly present in the blood at the 

 termination of the septicemia (Hauduroy-^^). They have been isolated 

 from the water of a number of rivers (Beckerich and Hauduroy^^). 



3. B. paratyphosus A (Salmonella paratyphi) 



Everything which has been said with regard to B. typhosus applies 

 to paratyphoid A, although the latter bacillus has received much less 

 study. 



* Complete inagglutinability is only observed, as we have seen in connection 

 with dysentery bacilli, when the resistance is absolute. Agglutinability is 

 restored gradually as the resistance is gradually lost. 



t When the term resistant bacteria is used without qualification it should be 

 understood that it invariably refers to "bacteria possessing an acquired resis- 

 tance, in ultrapure culture." 



