BEHAVIOR OF BACTERIOPHAGE IN DISEASE 463 



bacteriophage is of prognostic significance. It is sufficient to test 

 simultaneously the virulence of the intestinal bacteriophage of the 

 patient for B. coli, for the pathogenic bacillus taken from the patient, 

 and for a stock culture of B. typhosus. A comparison of these three 

 results furnishes the information desired. The detection of resistance 

 in the pathogenic bacterium would indicate a poor prognosis, and that 

 in proportion as the resistance is the more pronounced. The establish- 

 ment of a refractory state in the bacterium, resulting in the formation 

 of a mixed culture in the intestine accompanying a septicemia, implies .a 

 fatal outcome and suggests that death will not be long delayed. 



If we consider all of the data which have been presented with refer- 

 ence to the relation of the bacteriophage to typhoid fever, we may 

 summarize the results somewhat as follows: 



In all of the cases of typhoid fever studied, whatever may have been 

 their severity, the appearance in the intestinal bacteriophage of a 

 virulence for the pathogenic bacillus has been preceded by an increase 

 in virulence for B. coli. This has always begun in the course of the 

 second week and has rapidly attained great intensity. This activity 

 was maintained during the entire course of the infection and appreciably 

 decreased only during convalescence, sometimes even later. On the 

 contrary, the development of a virulence for the pathogenic bacillus 

 has varied according to the severity of the disease. In cases that were 

 mild or of average severity the activity of the bacteriophage for this 

 bacillus appeared before the end of the second week and disappeared 

 toward the end of convalescence. The activity for B. coli and for B. 

 typhosus is, in these cases, parallel. In the severe cases an activity for 

 the typhoid bacillus only began to manifest itself in an energetic man- 

 ner towards the beginning of definite improvement. It persisted for a 

 greater or less length of time, in some cases up to the middle of the period 

 of convalescence. 



In the forms with relapse and recrudescence the struggle was com- 

 plicated by the fact of the acquisition of a resistance by the bacteria, 

 and it was only toward the decline of this relapse that the virulence of 

 the bacteriophage was sufficient to definitely control the resistance of 

 the bacterium. Here, the activity of the bacteriophage was main- 

 tained up to complete recovery, that is to say, up to the moment when, 

 because of a total destruction of the pathogenic bacteria, the bacterio- 

 phage was no longer able to develop at their expense. 



In all cases, the condition of the patient faithfully registered the 

 vicissitudes of the struggle taking place within the body between the 

 bacteriophage and the invading bacterium. 



