BEHAVIOR OF BACTERIOPHAGE IN DISEASE 451 



of a resistant race of the latter. As a result there is a struggle, and the 

 condition of the patient reveals the fluctuations of the struggle. 



This conflict is particularly to be noted in cases of long duration with 

 a relapse. During the latter, especially, the virulence of the bacterio- 

 phage shows daily fluctuations. At certain times it may be extreme 

 for the stock culture, although uniformly very weak for the strain 

 causing the infection. Recovery begins to take place at the moment 

 when the bacteriophage shows an activity as intense for one strain as 

 for the other. 



Under two circumstances the disease may have a fatal issue : 



1. When the bacteriophage exerts no protective action through a lack 

 of adaptation to the pathogenic bacillus. Here there is no struggle at 

 all, and the bacterium develops freely. In the great majority of such 

 cases non-adaptation is the cause of death, which then occurs quickly. 



2. In certain exceptional cases the pathogenic bacterium acquires 

 an almost absolute resistance, — a refractory state. And the bacterio- 

 phage, whatever the degree of virulence it acquires, remains ineffective. 

 From this moment, when the bacterium becomes equal to the bacterio- 

 phage, the entire body is invaded and death ensues after a greater or 

 less length of time. 



3. THE BACTERIOPHAGE IN TYPHOID FEVER 



Several cases of typhoid fever of varied severity have been studied 

 by the same method as that employed in bacillary dysentery. Fourteen 

 of these were in the Pasteur Hospital for treatment, and of these the 

 stools were examined at least once a day throughout the course of the 

 disease and during convalescence. Fourteen more, under treatment 

 in other hospitals, were followed with somewhat fewer examinations. 

 In all of the charts which follow, the following data are presented;^ 

 in the upper portion is the curve showing the temperature ; in the lower 

 portion there are three tracings, (1) in dotted line, showing the curve 

 of the virulence of the bacteriophage for B. coli, (2) in broken line, 

 showing the virulence of the bacteriophage for an old laboratory strain 

 of B. typhosus, a strain which has undergone a great many transfers 

 on laboratory media (this same strain was used in all the cases studied), 

 and (3) in solid line, indicating the curve of virulence of the bacterio- 

 phage for the strain of B. typhosus from the patient himself, isolated 

 either by stool culture or by blood culture. 



In order to use bacilH as comparable as possible with those found in 

 the body of the patient the strains were transplanted as infrequently 



