424 THE BACTERIOPHAGE AND ITS BEHAVIOR 



albus, or B. proteus, either in the meconium or in the stools of infants 

 up to the 4th day. 



Suranyi and Kramar^^^ have made some systematic studies of the 

 same nature. They uniformly failed to find the bacteriophage in the 

 meconium, and in no case could one be demonstrated in the stools of 

 the infant before the 4th day. It may be added that in the course of my 

 studies I have had occasion to examine 4 infants, aged, respectively, 

 7, 9, 10, and 12 days. In each of these cases I found a bacteriophage- 

 B. coli symbiosis. 



One might conclude from these studies that the bacteriophage makes 

 its appearance in the intestine of man between the 4th and the 7th days 

 after birth. It is probable that its appearance coincides with the inges- 

 tion of a colon bacillus infected with a bacteriophage protobe. 



3. THE BACTERIOPHAGE IN ANIMALS 



It is much easier to prove that the bacteriophage is normally present 

 in the intestinal tract of animals than in man, for in domestic animals 

 certainly, the virulence is rarely limited to B. coli, but extends to the 

 dysentery strains and to the paratyphoid bacilli (d'Herelle,^^^-^^''). 



This difference in the nature of the virulences of the intestinal bac- 

 teriophage in man and in the animals can hardly be explained except 

 in a single way, — because of their mode of life the animals are much 

 more exposed to the frequent ingestion of different bacilli. In animals 

 the bacteriophage is found constantly, therefore, in the presence of 

 varied species of bacteria, and against these it builds up its faculty of 

 virulence. 



This hypothesis receives support from the fact that although the 

 intestinal bacteriophage of animals which hve an unconfined life almost 

 always manifests multiple virulences, with laboratory animals, re- 

 stricted to their own cages and under conditions more closely approach- 

 ing those of human beings, the virulence is often restricted to the in- 

 testinal colon strain. 



We will see later that in a group of persons exposed to the possible 

 ingestion of a pathogenic bacillus, we find that in all of them the in- 

 testinal bacteriophage manifests a virulence for the bacillus in question. 

 Confirming this observation, the following tables will show us that 

 in animals which find themselves in an environment contaminated by a 

 bacterium, even though the organism is not pathogenic for the animal 

 in question, we find that the intestinal bacteriophage acquires a viru- 

 lence for this bacterium, while in all of the animals of the same species 



