64 THE BACTERIOPHAGE AND ITS BEHAVIOR 



fied by the introduction of gelatin into the medium; with others, on 

 the contrary, the same medium prevents multiphcation completely. 

 Brutsaert^^" has confirmed this observation. 



Again and again we are confronted by the same conclusion: the 

 most important factor in bacteriophagy is the quality of the bacterio- 

 phage under consideration. 



A final explanation for the inhibitory action of gelatin has been 

 provided by Hauduroy.^^^ He states, "It is solely the high viscosity 

 of the medium containing gelatin which interferes with the production 

 of the phenomenon." He showed, in fact, while working with several 

 substances, such as the gums and egg albumin, having the property of 

 augmenting viscosity, that the inhibition is a direct expression of the 

 viscosity, quite unrelated to the chemical nature of the viscous sub- 

 stance. To attribute this inhibition of bacteriophagy to anything 

 other than a reaction between colloids, allied to other reactions of this 

 type, is impossible. In no case is the bacteriophage destroyed. After 

 a period of contact of any duration it is only necessary to dilute the 

 medium with bouillon, thus diminishing its viscosity, to permit the 

 inception of the process of dissolution. 



Certain experiments which I have made, confirming fully these 

 conclusions of Hauduroy, may be mentioned. 



To 10 cc. of a peptone bouillon containing 0.8 per cent salt, is added 

 20 per cent of gelatin. The pH is then adjusted to 7.8. With the 

 medium at a temperature of 35°C., Staphylococcus aureus is introduced 

 to give a concentration of about 200 miUion organisms per cubic centi- 

 meter. It is then inoculated with 0.05 cc. of a highly active bacterio- 

 phage filtrate, that is, with one capable of regularly causing a total and 

 yeimanent dissolution of a normal suspension in bouillon. After incu- 

 bation for 6 days at 35°C. the medium was perfectly limpid, dissolu- 

 tion was complete. In a control mixture in plain bouillon, without 

 gelatin, dissolution was completed in 24 hours. The conclusion is 

 obvious. When added in a sufficient quantity to a medium in which 

 bacteriophagy should be effected, gelatin completely inhibits the 

 action of races of the bacteriophage of low activity, while for more 

 potent races the process is retarded, and the number of bacteria dis- 

 solved is the greater as the bacteriophage is the more powerful.* With 



* With the acquisition of a resistance by a portion of the bacteria, an acquisi- 

 tion favored by the delay associated with the viscosity of the medium, we are not 

 now concerned, yet in this connection the retardation is of considerable signifi- 

 cance. This feature of the reaction will receive further attention when we deal 

 with the behavior of the bacterium toward the bacteriophage. 



