THE BACTERIOPHAGE CORPUSCLE 83 



After 48 hours, 3 of these suspensions are clear (this is the average of 

 7 experiments of 10 tubes each, made with the same bacteriophage fil- 

 trate). The other 7 are turbid, and repeated control tests show that 

 they contain normal cultures of dysentery bacilh. The result is, then, 

 complete bacteriophagy in 3 suspensions and complete absence of bac- 

 teriophagy in the other 7 (d'Herelle^^^). 



This experiment settles the question. If the bacteriophage was to 

 be found in a state of solution in the 10~i° dilution, it is obvious that 

 each of the 10 cc. of this dilution would have contained a tenth part of 

 it, that is, none of the 10 cc. would have been favored. Each would 

 have contained a like quantity, and all of the 10 suspensions, each receiv- 

 ing one of these 10 cc, would have behaved in the same manner; 

 they would have been the seat of a comparable phenomenon. But 

 this is not the case, as shown by the fact that 3 suspensions undergo 

 bacteriophagy, while 7 do not. There is, then, among the 10 cc. dis- 

 tributed in equal amounts among the ten suspensions, 3 portions of 

 1 cc. each which contained the bacteriophage principle. In the other 7 

 it was lacking. This is an absolute proof that the bacteriophage exists 

 in discontinuous form, that is to say, in corpuscular form.* 



Experiments of this type always yield the same result, regardless of 

 the bacterial species involved, provided the bacteriophage principle 

 be very active. The single difference that may appear among the differ- 

 ent experiments is due solely to the fact that different filtrates do 

 not all contain the same number of bacteriophage corpuscles per cubic 

 centimeter. Sometimes the dilution will be 10~^, sometimes 10"^ 

 often 10-^ or 10-^", and rarely 10~i\ which, when distributed in equal 

 portions among a number of bacterial suspensions, will provoke bac- 

 teriophagy in a certain number of these suspensions, leaving others 

 untouched. 



Inasmuch as the concept of the corpuscular nature of the bacterio- 

 phage dominates entirely the study of this principle, I believe it wise to 

 introduce the protocols of a few other experiments, taken at random 

 from among more than fifty which I have performed, and which, uni- 

 formly, have given the same results as regards the demonstration of the 

 corpuscular state. 



* During my residence at the University of Leiden, in discussing this question 

 with my colleague, Professor Einstein, he told me that, as a physicist, he would 

 consider this experiment as demonstrating the discontinuity of the bacteriophage. 

 I was very glad to see how this deservedly-famous mathematician evaluated my 

 experimental demonstration, for I do not believe that there are a great many 

 biological experiments whose nature satisfies a mathematician. 



