NATURE OF BACTERIOPHAGE 333 



3. THE AUTONOMY OF THE BACTERIOPHAGE CORPUSCLE 



If the being, whose nature is in question, is macroscopically or micro- 

 scopically visible, it is not, usually, difficult to ascertain if it possesses 

 the power of assimilation of a heterologous medium. When a bacte- 

 rium multiplies within the body of an animal or in bouillon, we conclude 

 that it has transformed the animal substance or the nutritive substances 

 of the artificial medium into "bacterium substance," and that, there- 

 fore, it possesses the power of assimilation in a heterologous medium. 



If the being whose nature we desire to determine can not be seen 

 because of its smallness, does the mere matter of size preclude the possi- 

 bifity of determining whether or not it has this power? Not at all. 

 For in either case we do not see the assimilation. We deduce that it 

 must occur because the being in question multiplies, using a heterologous 

 substance in order to build up its own substance. 



The bacteriophage corpuscle multiplies at the expense of the bacte- 

 rium substance. Everyone admits this, and if the corpuscles were visible 

 no one would question but what the process were one of assimilation. 

 But in the case of the bacteriophage, and indeed, this is true for all 

 ultraviruses, it may be objected that the substance of the corpuscle may 

 be bacterial substance. In such a case the process would be a simple 

 assimilation of a homologous medium, as in the case of the crystal which 

 multiplies in a concentrated solution of a salt. Consequently, in order 

 to demonstrate that the bacteriophage corpuscle assimilates when in a 

 heterologous medium, it is necessary in the first place to show that 

 ''bacteriophage substance" differs from "bacterium substance," that 

 is to say, it is essential to demonstrate that the bacteriophage corpuscle 

 is an autonomous being, independent of the bacterium which undergoes 

 its action. 



Proofs of the autonomy of the bacteriophage corpuscle are both many 

 and varied. Some of them will be presented in the next few pages. 



I. Since the beginning of my study of the bacteriophage I have iso- 

 lated more than 100 races of the Shiga-bacteriophage from the stools 

 of normal men or from patients convalescent from dysentery and other 

 diseases; from the excreta of a variety of animals, — sheep, swine, cattle, 

 dogs, cats, rabbits, chickens, ducks, geese, etc. — from the water of rivers 

 and wells, from tap-water, and from the sea, and I have yet to find two 

 races of the bacteriophage which are strictly identical as to their powers 

 of attack and as to the intensities of their action upon different species of 

 the colon-typhoid-dysentery group of organisms.^'^ This is true despite 

 the fact that throughout these investigations I have always employed 



