NATURE OF THE BACTERIOPHAGE 145 



determine the nature of this principle, and it was only after I 

 had considered all possible a priori hypotheses, multiplying the 

 control experiments which had demonstrated experimentally 

 with certainty that the principle could be only an autonomous 

 living being, a filtrable microbe parasitizing the bacteria, that 

 I resolved to publish, in 1917, the first communication announc- 

 ing the discovery of an ultramicrobe parasitizing the dysentery 

 bacillus. In this report I gave the principal characteristics of 

 the virus and indicated the role played by it in the course of the 

 disease. From 1917 to the end of 1919, I continued these in- 

 vestigations alone, extending them to other diseases, and it was 

 only in December 1919 that Kabeshima, working in my labora- 

 tory with strains which I had furnished him, published results 

 which confirmed mine. Since that time, investigations on the 

 bacteriophage have multiplied, and rare indeed are the labora- 

 tories which are not interested in the question. 



It may seem strange, at first sight, that I should have been 

 able to work alone on this question for such a long time; a cir- 

 cumstance which has permitted me to establish the facts in their 

 entirety, and the relation between them; to demonstrate their 

 importance from the point of view of immunity, and to accom- 

 plish this before any other communication appeared. In this I 

 have been favored by circumstances and even by the strangeness 

 of the facts themselves, which at first excited, not merely astonish- 

 ment, but incredulity, even among my most friendly colleagues, 

 who were not loath to consider me a visionary. This time has 

 passed. The facts are recognized to be correct. The most 

 recent work appears to affirm the curative properties of cultures 

 of the bacteriophage. The only point at issue is my conception 

 of the nature of the active principle. 



I may be permitted to make a few remarks upon the subject of 

 this discussion. All authors, without exception, who have formu- 

 lated an hypothesis regarding the nature of the bacteriophage 

 have adopted a method of reasoning that is somewhat peculiar. 

 None of them have taken the trouble to review the experiments 

 that I had accumulated in favor of the living nature of the bac- 

 teriophage during the years that I had alone been occupied with 

 this question ; experiments moreover, which in no instance are open 



