420 THE BACTERIOPHAGE AND ITS BEHAVIOR 



organism means rather that the strain is not susceptible, and not that 

 the bacteriophage is absent. And from this and other studies ^^^' ^i"- ^-^ 

 I have concluded that the bacteriophage is constantly present in the 

 intestinal tract of all normal men, where it grows at the expense of B. 

 coll and perhaps of other banal bacteria found there. 



These conclusions have been subjected to attack by several authors, 

 and even by some of those who have found the bacteriophage in normal 

 men, their argument being that the condition is not habitual. 



Recently I have carried out some more of these studies, following a 

 a different and more rational method. In its essentials this method in- 

 volved the following procedures, all carried out with the same speci- 

 men of fecal material. 



First, a filtrate is prepared, according to the usual technic, which has 

 been described. 



Second, the bacteria of the stool are isolated on Endo medium. 

 After incubation, it is found that the reddish colonies of B. colt assume 

 three different forms, 



(a) those perfectly circular, with a rounded surface ; 



(6) those perfectly circular, umbilicated; 



(c) those which are irregular and flat. These last are, in general, 

 mixed colonies. 



Twelve of the circular colonies are removed and transferred to tubes 

 of bouillon. At the same time, if any colorless colonies are present 

 on the plates, three or four of these are also transferred to bouillon tubes. 

 To each of these implanted tubes 3 drops of filtrate are added, and the 

 tubes are incubated at 28 to 30°C. 



After incubation for 24 hours each tube is examined for the presence 

 of the bacteriophage, by spreading the culture on agar, and, if neces- 

 sary, by making two or three passages, always at the expense of the 

 B. coli derived from the colony which was used to seed the first tube. 



During a period of three months, at irregular intervals, I secured 17 

 specimens of the feces of a normal person.* 



In each of the 17 specimens the bacteriophage protobe was present. 

 But the proportion of susceptible colonies of B. coli found on the plates 

 varied from one examination to another. In this respect, the results 

 were: 



In 1 specimen, 5 of the 12 colonies were susceptible; 



* The same person who had provided the specimens which gave the results 

 incorporated in table 55. As a matter of fact, he is the author of these lines. 

 When these specimens were examined he was living at Alexandria, as were the 6 

 individuals mentioned in a later paragraph. 



