46 THE BACTERIOPHAGE AND ITS BEHAVIOR 



A correlation of all of these findings shows, therefore, that the opti- 

 mum pH varies (o) with the bacterial species involved, (6), with the 

 race of the bacteriophage reacting upon it, and (c) with the composition 

 of the medium in which the reaction takes place. Nevertheless, it is 

 possible to say that, in general, a slight alkalinity of the medium pro- 

 vides a favorable condition. Hence, unless one has in view some 

 special investigation demanding particular conditions, the best medium 

 for routine purposes is the ordinary peptone bouillon "with a reaction 

 of pH 7.8. 



Bacteriophagy will take place in synthetic media provided these 

 permit the growth of the bacteria against which the bacteriophage is 

 to act. Here the conditions as regards alkalinity are the same as in 

 bouillon. The formula for such a medium, suited to the growth of 

 B. coli, as well as to some, but not all, strains of B. dysenteriae, is: 



Water 100 cc. 



Sodium chloride 0.5 gram 



Potassium phosphate 0.1 gram 



Asparagine 0.5 gram 



The reaction to be adjusted in accord with the experiment to be 

 performed. 



Another medium, suggested by Gratia^^^ for B coli is: 



Water 1000 cc. 



Glycerin 30.0 cc. 



Sodium chloride 5.0 grams 



Calcium chloride 0.1 gram 



Magnesium sulfate 0.2 gram 



Dipotassium phosphate 2.0 grams 



Ammonium lactate 12.0 grams 



The reaction adjusted to pH 7.4. 



4. EFFECT OF THE CONDITION OF THE BACTERIUM 



If we take, then, 10 cc. of this beef bouillon, containing peptone and 

 salt, adjusted to pH 7.8, and suspend some dysentery baciUi of the 

 Shiga-Kruse type removed from an agar slant which had been planted 

 some 18 to 24 hours previously, to provide a suspension containing 

 approximately 250 million per cubic centimeter, and further, inocu- 

 late this suspension with a trace (0.001 cc, for example) of a filtrate 

 containing a bacteriophage very active against B. dysenteriae, we will 

 find, after incubation at 37°C., that within a few hours, from 4 to 24, 



