BACTERIOPHAGY IN A FLUID MEDIUIVI 65 



races possessing a maximum activity all of the bacteria are destroyed 

 and dissolved. The role of gelatin, in the last analysis, consists solely 

 in altering the rate of the phenomenon, that is, in extending the dura- 

 tion of the action. 



All neutral substances, which possess the property of augmenting 

 viscosity, affect the phenomenon of bacteriophagy as does gelatin, 

 and the intensity of this effect is in direct proportion to the viscosity 

 of the medium. 



In the particular case under consideration the course of the phenom- 

 enon is regulated by variations in two factors, the degree of activity 

 of the bacteriophage involved, and the viscosity of the medium. 



7. EFFECT OF THE CHEMICAL CONDITIONS OF THE MEDIUM 



Colloids 



We have seen that gelatin, and this is also true for the gums and 

 for egg albumin, have of themselves no effect upon bacteriophagy. 

 It is only when such substances are added to the medium in a quantity 

 sufficient to significantly augment the viscosity that they exert an 

 effect, and even then this effect is simply a retardation of the action. 

 Certainly this is the case when a potent bacteriophage is used. 



It is of interest, in comparison with the above, to observe the effect 

 exerted by a colloid which does not modify the viscositj^ of the medium 

 to which it is added and whose action, if any, must be due to properties 

 inherent in the colloid itself. For this purpose I have chosen colloidal 

 silver (collargol, Clin, as provided in ampoules for purposes of injection). 



The following experiment indicates the nature of the effects with 

 such a colloid. To 8 cc. of Liebig's extract bouillon, made up with 

 1 per cent of peptone and 0.8 per cent of salt (reaction pH 7.6) collargol 

 is added. Three tubes are prepared. The mixtures are implanted 

 with a heavy suspension of Staphylococcus aureus derived from a young 

 culture, the final concentration being 100 milhon organisms per cubic 

 centimeter. Each of the suspensions is then inoculated with 0.02 cc. 

 of a Staphylo-bacteriophage, and the tubes are incubated at 32°C. 



The appearance after 24 hours is as follows : 



