UNICITY OF BACTERIOPHAGE PROTOBE 361 



here disclosed to the protobes, beings even more simple than the bacteria, 

 and to ascertain whether these facts accord with their behavior. 



It might be assumed, a priori, that there is "one" assimilation, that 

 is to say, that the process always ends in the formation of a single sub- 

 stance and that this substance is identical with the substance of the being 

 which assimilates. The facts are not in accord with this point of view. 



When one supphes a metazoan provided with a speciahzed digestive 

 tract any food material, from either the animal or the vegetable king- 

 dom, which it is able to assimilate the assimilation is always complete, 

 that is, the process ends in the formation of substances identical with 

 those of which the metazoan is composed. Is the process the same in 

 microorganisms, in particular, in the bacteria? Obviously not, for 

 there is proof to the contrary. It is only necessary to provide a bac- 

 terium with different food materials to cause transformations in its 

 antigenic properties, and this effectively shows that the constitution of 

 the "substance" of this bacterium varies according to the nutritive 

 materials which it assimilates.* 



Here is the proof of his last statement, the experiments cited being 

 those reported by Brocq-Rousseu, Urbain, and Forgeot.f 



For a long time we have known that a streptococcus, by passages 

 through an animal, becomes what is termed a "passage streptococcus," 

 but these authors should receive the credit for showing the nature of 

 this transformation. 



They utilized in their experiments a strangles antiserum (an anti- 

 streptococcus serum, specific for the streptococcus of equine strangles) 

 which when titrated by the method of Calmette and Massol contained 

 1500 units of antibody. The antigen used consisted of a suspension 

 of the streptococci killed by alcohol-ether, prepared in such a way that 

 there was 1 cgm. of the bacterial bodies to 20 cc. of 0.9 per cent phys- 

 iological saline. 



Different animals were injected with different strains of the strangles 

 streptococcus recently isolated from the lesions of infected horses. The 

 strains were not passed through any other animal after isolation. For 

 the injections they adopted the subcutaneous route with mice, the 

 pleural route with rats, the intraperitoneal route with guinea pigs, and 

 the intravenous or intraperitoneal routes with rabbits. 



* This transformation in antigenic properties is a commonly observed fact. 

 The following paragraphs, dealing with variations in the antigenic properties of 

 microorganisms and of protobes, will present typical examples. 



t Brocq-Rousseu, Urbain, and Forgeot. — Etudes sur le streptocoque gour- 

 meaux. Ann. Inst. Pasteur, 1923, 37, 322. 



