40 THE BACTERIOPHAGE AND ITS BEHAVIOR 



variable. Races of the bacteriophage may be isolated which are ex- 

 tremely active, causing within a few hours a total dissolution of all of 

 the bacteria contained in a culture or in a rather turbid suspension. 

 On the other hand, other races may not cause any detectable dissolu- 

 tion, and it is only by spreading the mixtures of bacteriophage and 

 bacterium upon an agar medium that their presence can be disclosed. 

 More will be said upon this point in Chapter IV and those following. 



Let us leave, for the moment, the study of these slightly active 

 races and consider in these first three chapters only the typical phe- 

 nomenon of bacteriophagy, that is, the phenomenon leading to a total 

 dissolution of the bacteria of a young culture or a suspension of hving 

 organisms. 



Whatever may be the bacterial species involved, under the action 

 of an active bacteriophage the phenomenon of bacteriophagy manifests 

 itself always in the same manner. 



But the diverse races of the bacteriophage, active upon different 

 bacterial species, are more or less frequent in nature and more or less 

 easy to disclose. The bacteriophage which it is always easy to pro- 

 cure, in whatever place it may be found, is that which causes bacteri- 

 ophagy of Shiga dysentery bacilli, and it is for this reason that, in the 

 majority of the experiments to be recorded, I will take as types this 

 race of the bacteriophage and this bacterium. One may isolate, with 

 certainty, a race of the bacteriophage always very active against dysen- 

 tery bacilli from the excreta of a convalescent from bacillary dysentery, 

 often, indeed, from the fecal discharges in a case of any acute intestinal 

 disease. Furthermore, such races are to be found in the excreta of 

 the majority of horses and domestic fowls, even when in a normal 

 state of health. 



2. SERIAL ACTION 



The basic experiment, as recorded in the Introduction, has shown 

 that the bacteriophagous principle reveals itseK through bringing 

 about the dissolution of bacteria. But, and this is a distinctive pecu- 

 liarity of this action, it is only in proportion as this dissolution is effected 

 that the bacteriophagous principle, which is the cause of it, reproduces 

 itself ^ — multiplies . 



To demonstrate this phenomenon of serial activity a small quantity 

 of bacteria are removed from a young agar slant culture and suspended 

 in bouillon in such a concentration as to produce an obvious turbidity. 

 A platinum inoculating needle is then dipped in a "bacteriophage fluid" 



