188 THE BACTERIOPHAGE 



1. The bacteriophage shows no, or but slight, activity as long 

 as the condition of the patient remains stationary. The improve- 

 ment occurs when the activity of the bacteriophage manifests 

 itself in an energetic manner, not only for the stock cultures of 

 the bacillus but also for the strain derived from the patient. 

 There has been a delay in the adaptation, then a sudden acquisi- 

 tion of a high virulence. Recovery takes place promptly, for the 

 pathogenic bacterium is not able to develop a resistance. 



2. At a given moment of the disease the virulence of the bac- 

 teriophage manifests a more or less energetic action on the stock 

 bacilli, but on the contrary, it is inappreciable or but very weak 

 on the strain taken from the patient. Here there has been a de- 

 lay in the adaptation, since the bacteriophage has gradually ac- 

 quired virulence for the pathogenic bacillus, but this has allowed 

 sufficient time for the creation 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 dura- 

 tion with a relapse. During the latter, especially, the virulence 

 of the bacteriophage shows daily fluctuations. At certain times 

 it may be extreme for the stock culture, although uniformly very 

 weak for the strain of 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. 



The disease has a fatal issue in two cases : 



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 ac- 

 quires an almost absolute resistance, a refractory state. And 

 the bacteriophage, whatever the degree of virulence it acquires, 

 remains ineffective. From this moment, when the bacterium 

 becomes equal to the bacteriophage, the entire body is invaded 

 and death ensues after a greater or less length of time. 



