172 THE BACTERIOPHAGE AND ITS BEHAVIOR 



of the bacteriophage which manifests these multiple virulences is most 

 certainly derived from a single corpuscle, the effects can hardly be said 

 to be due to a mixture of races. 



The fact that multiple virulences persist despite a great many pas- 

 sages made at the expense of a single bacterial strain, is, however, the 

 most vahd evidence that these multiple virulences are attributes of a 

 single bacteriophage corpuscle. Let us assume that a stool filtrate 

 causing bacteriophagy of several bacteria of different species contains 

 several races of the bacteriophage. If, with this filtrate, we carry out 

 passages at the expense of a single bacterium we must admit that only 

 those corpuscles should multiply which possess a virulence for this bac- 

 terium. We must hkewise admit that all corpuscles avirulent for this 

 bacterium should disappear gradually in the course of the passages. 

 And the number of passages necessary to eliminate all of the avirulent 

 corpuscles within the initial filtrate is readily calculable. Physicists 

 have determined that the smallest possible quantity of matter is the 

 electron, whose mass is 1-10~" grams. When, as the result of succes- 

 sive dilutions such as take place from passage to passage, we introduce 

 into a suspension a quantity of the initial filtrate less than 1-10~" grams 

 we may be very sure that there no longer remains any of the original 

 filtrate, and, a fortiori, none of the bacteriophage corpuscles which were 

 in this filtrate. All of these corpuscles present at this time result from a 

 multiplication of virulent corpuscles. In carrying out the series of 

 passages by introducing into the first suspension 0.001 cc. of filtrate, 

 into the second 0.001 cc. of the first suspension after it has undergone 

 bacteriophagy, and continuing thus, introducing each time 0.001 cc. 

 of the last suspension dissolved into 10 cc. of fresh bacterial suspension, 

 it can be readily calculated that in the seventh passage there can be but 

 1-10~2^ grams of the original filtrate, that is to say, a virtually non- 

 existent quantity, since it is smaller than an electron. This seventh 

 suspension can not contain any of the bacteriophage corpuscles aviru- 

 lent for the bacterium at the expense of which the passages were made, 

 even though such corpuscles were found in the original filtrate. If 

 the corpuscles found in the last filtrate manifest a virulence for a bac- 

 terium of a species other than that with which the passages were made the 

 only inference is that these corpuscles possess the property of causing 

 a bacteriophagy of different bacterial species at one and the same time. 



But experiment shows that, not only after the seventh, but after more 

 than 1000 passages, a race of the bacteriophage still possesses the prop- 

 erty of causing bacteriophagy with bacteria belonging to different 



