BACTERIOPHAGY IN A FLUID MEDIUM 49 



Although, as has been stated above, bacteriophagy will not take place 

 with dead bacteria, this does not mean that it is essential that the 

 bacteria be young. Various authors (Kuttner^^^ first, and later Bordet 

 and Ciuca®^) have suggested that bacteriophagy can only be effected 

 when the bacterium is in process of division. That the moment of 

 division represents the most critical period for the bacterium, that 

 bacteriophagy takes place much more actively when the bacteriophage 

 acts on young bacteria, was stated among the very first of my reports. 

 But it is none the less true that old bacteria, certainly no longer dividing, 

 can undergo bacteriophagic dissolution, as has been shown in the 

 experiments presented above. Moreover, this fact has been confirmed 

 by Maitland,*^2 working with organisms of the typhoid-dysentery 

 group, and more recently by collaborators of Bordet (Gratia and 

 Rhodes^^^). Gratia combined a Staphylo-bacteriophage of a very high 

 potenc}^, using an extreme dilution of the filtrate, with a suspension of 

 Staphylococcus aureus, and observed, under these conditions, that bac- 

 terial dissolution commenced only after about a week. The dissolution 

 was, nevertheless, complete. He concluded quite rationally that 

 bacteriophagy may take place with bacteria which are no longer 

 reproducing.* 



From these facts it may be deduced, in brief, that whatever the 

 bacterial species, bacteriophagy may take place with a bacterium 

 of any age, provided it be alive and normal. Yet, although all hving 

 unaltered bacteria are susceptible, the critical moment, the period 

 when the bacterium is most vulnerable, is the moment of division. 



5. EFFECTS OF THE RELATIVE CONCENTRATIONS OF BACTERIO- 

 PHAGE AND BACTERIA 



Let US now consider the variable characteristics attending the phe- 

 nomenon of bacteriophagy when it occurs under different concentration 



* Gratia and Rhodes even add that the reaction occurs with bacteria in process 

 of disintegration, since microscopic examination showed that after a week modi- 

 fied staphylococci were present. That these degenerating staphylococci had 

 been dissolved is certain, since the medium ultimately became completely clari- 

 fied, but to assume that the dissolution of these altered bacteria was brought 

 about directly, by the bacteriophage itself, is another question. This possibility 

 we will have occasion to treat at some length when we consider the mode of action 

 of the bacteriophage. Here, let us simply say that the dissolution of modified 

 bacteria, and dead cells as well, appears to be effected through the action of 

 substances which become disseminated in the medium during the course of 

 bacteriophagy. 



