VIRULENCE OF THE BACTERIOPHAGE 99 



only a few were endowed with a latent virulence sufficient to 

 parasitize the new bacterium offered them and to multiply at 

 its expense. 



The persistence of latent virulence is the appanage of certain 

 particularly apt individuals. With each passage, at the expense 

 of the new bacterium, these individuals multiply, their virulence 

 becomes enhanced, and finally, after a sufficient number of pas- 

 sages, a complete lysis of the suspension is secured. 



With these facts as a basis, an attempt has been made to adapt 

 to the dysentery bacillus a strain of bacteriophage active for the 

 staphylococcus, although the ultramicrobe at first appeared de- 

 void of all action on the dysentery strain. In this attempt, ten 

 drops of an active anti-staphylococcus bacteriophage were inocu- 

 lated into a double suspension containing in each cubic centimeter 

 ten million staphylococci and ten million B. dysenteriae. After 

 twelve passages (each passage being separated by a bougie filtra- 

 tion and twelve drops of the filtrate inoculated into a fresh 

 staphylococcus-dysentery suspension) the bacteriophage very 

 actively attacked the dysentery bacillus. This property de- 

 veloped very abruptly during the eleventh passage. After a 

 series of twenty passages made in conjunction with Shiga alone 

 the bacteriophage did not possess any activity for the staphylo- 

 coccus, and it has been impossible to cause it to reassume such 

 activity. 



Up to the present time it has been impossible to accomplish 

 the inverse experiment, that is, to cause a bacteriophage active 

 for the Shiga bacillus to acquire a virulence for the staphylococcus. 



This inequal persistence of latent virulence of the bacteriophage 

 against diverse species of bacteria may be explained. The in- 

 testinal bacteriophage maintains itself in the intestinal tract at 

 the expense of the different intestinal bacteria. The bacterio- 

 phage is therefore, in reality a normal parasite of the colon- 

 typhoid-dysentery group and an accidental parasite of the other 

 bacteria against which it acquires virulence in the same environ- 

 ment, as a result of conditions at present undetermined. It can 

 be understood then, that a bacteriophage active, when derived 

 from the body, for an organism rather remote from the colon- 

 typhoid-dysentery group, for example, a staphylococcus, retains 



