BACTERIOPHAGY IN A FLUID MEDIUM 55 



trations. For B. gallinarum and the different Pasteurella organisms, 

 the maximum titre is the same. With B. pestis, it has been impossible 

 to go above a limit of 200 million per cubic centimeter. But here we 

 must bear in mind that with B. dysenteriae and the staphylococcus, 

 except for the extremelj^ active races of the bacteriophage, the maxi- 

 mum number capable of complete dissolution is only 350 to 400 million 

 per cubic centimeter, and it is quite possible that for B. coli, B. typhosus 

 B. pestis, etc. a complete dissolution of more concentrated suspensions 

 might be obtained with races of the bacteriophage still more active 

 than those which I have isolated and worked with up to the present 

 time. 



In bacteriophagy all is relative; all depends upon the aptitudes, the 

 qualities, of the race of bacteriophage with which one is working. Too 

 many authors seem to forget this. 



Limits of activity of the bacteriophage principle 



What are the maximum and minimum quantities of the bacterio- 

 phage with which bacteriophagy can be effected? 



The phenomenon takes place if bacteria are suspended in an undi- 

 luted bacteriophage filtrate. It is unnecessary to support this state- 

 ment by citing experiments, particularly since those described upon 

 the preceding pages demonstrate this adequately. They show that 

 it is possible to add a new quantity of bacteria to a medium resulting 

 from a complete dissolution of bacteria and that they are in turn 

 entirely dissolved. 



Experiments upon the lower limit are more interesting. Let me 

 say once more that the condition portrayed here applies only to races 

 of the bacteriophage having a high potency.* 



* Although to some, these repetitions may appear quite uncalled for, experience 

 shows that they are necessary. For many workers, carrying out their experiments 

 under conditions other than those which I have indicated ha\e obtained results 

 differing from mine (it could hardly be otherwise) and have, upon this basis, felt 

 warranted in contradicting my experimental findings. For example, and this 

 example is selected from among many others, several investigators, early in their 

 studies, have affirmed that the dissolution of bacteria is never complete, a con- 

 clusion reached simply because of the fact that they used a bacteriophage of but 

 little activity. It is true that they have later recognized that a total dissolution 

 occurs, a fact which today is unanimously accepted. But despite the fact that 

 these authors have later revised their conclusions, it would have been somewhat 

 more logical to have worked first under the conditions as I described them. This 

 would have rendered unnecessary a subsequent retraction. 



