BACTERIOPHAGY IN A FLUID MEDIUM 45 



To return to the subject under consideration, that of the effect of 

 the reaction of a medium upon bacteriophagy, we will see that through 

 a process of adaptation it is possible to so alter the bacteriophage that 

 the processes of dissolution will take place in an acid medium. A 

 further discussion of this is reserved for a later section. It is mentioned 

 here simply to show the complexity of the conditions contributing to 

 bacteriophagy and to emphasize the impossibility of stating in a defi- 

 nite manner conditions such as will provide for optimum activity 

 regardless of the race of bacteriophage involved. It is certain, never- 

 theless, that in general an acid medium is but poorly suited to bac- 

 teriophagy. With the great majority of races of the bacteriophage 

 the phenomenon does not take place readily when the reaction of the 

 medium is acid (d'Herelle^^^). Scheidegger^^^ states that B. coli grows 

 normally in a bouillon with a pH of 4.5, even though the bacteriophage 

 is present. But under such conditions the principle is not destroyed, 

 for when such a medium is rendered slightly alkahne, bacteriophagy 

 occurs. 



While working with B. coli, investigating the process of bacteriophagy 

 occurring under particular conditions (when a very small number of 

 bacteria (simple seeding) in a peptone bouillon medium were mixed 

 with an indeterminate, but very great (10 drops) quantity of a filtrate 

 containing a but slightly active bacteriophage), Gratia-*^ noted that 

 the degree of alkalinity most favorable was found in the neighborhood 

 of pH 8.5. He states, however, that the phenomenon takes place in a 

 slightly acid (pH 6.8) medium. Scheidegger^^ also records bacteri- 

 ophagy in a medium of pH 6.5. 



These findings, together with other observations, show that the 

 optimal reaction is not a constant, varying not only with the bacterial 

 species and the race of the bacteriophage concerned, but differing also 

 with the nature of the medium. In testing a Flexner-bacteriophage, 

 acting upon its homologous bacterium, da Costa Cruz^^^ showed that 

 bacteriophagy could take place in Martin's bouillon with a reaction 

 of pH 6.5, but that to obtain a reaction of equal intensity in peptone 

 water it was necessary to adjust the reaction to pH 8.5, 



Using a Shiga-bacteriophage in conjunction with its homologous 

 organism, I have shown that in a peptone water (2.5 per cent), con- 

 taining 0.5 per cent of salt, with the pH at 7.5, a total dissolution of a 

 normal bacterial suspension takes place in 14 hours at 37°C. At pH 

 8.0 the dissolution is complete in 9 hours, and at pH 7.0 dissolution is 

 only partial. 



