NATUBE OF THE BACTERIOPHAGE 153 



9. It is impossible to isolate two strains of the bacteriophage 

 which are identical in the intensity of their action or in the scope 

 of their activity. With a single strain the intensity of the ac- 

 tion can be varied experimentally. Variation is an exclusive 

 characteristic of life. 



10. The lytic action is always exercised by one and the same 

 element as is demonstrated in the complement fixation reaction. 

 This element adapts itself to parasitism toward such and such a 

 bacterium, and the possibility of such adaptation necessarily 

 implies the living nature of the element which exercises it. 



11. Bruynoghe and Maisin have shown that the bacteriophage 

 is phagocytized and destroyed by the leucocytes. This fact 

 shows that the bacteriophage is foreign to the organism, and it 

 alone demonstrates that it can not be of leucocytic origin. 



The nature of the bacteriophage is not open to question; its 

 origin alone may be disputed. Is it an entirely autonomous being, 

 a "species", botanically or zoologically? Is it a " bioplast" 

 capable of indefinite reproduction at the expense of living bac- 

 teria, conducting itself as an autonomous being of which it has 

 all the properties? 



It is still impossible to decide this; experiment alone will de- 

 termine. However this may be, the two hypotheses, although 

 they may differ as to the origin of the bacteriophage, agree as to 

 its nature. The most probable interpretation is that the ultra- 

 microbe is autonomous, a botanic or zoologic " species." 



REFUTATION OF THE HYPOTHESIS OF KABESHIMA 



Without doubt readers will wish to know the diverse hypotheses 

 proposed by those who have opposed the living nature of the 

 bacteriophage, and I will discuss them in their chronological 

 order, although this may not be their documentary standing. 



Apart from the confirmation of the experiments which I alone, 

 or with my collaborators, have effected, these discussions repre- 

 sent about all that has been done on the question of the bacterio- 

 phage. By indicating these and commenting on them, this work 

 becomes completed and is a comprehensive statement of the 

 present knowledge regarding the bacteriophage. 



