68 THE BACTERIOPHAGE 



A result of this kind is usual when the filtrate is prepared from a stool 

 taken shortly before the manifestations of convalescence appear. 



(B) Ten cubic centimeters of the Shiga suspension are inoculated with 1 

 cc. of the filtrate prepared from the feces from the same dysentery patient, 

 but collected 24 hours later, the patient now being convalescent. Counts 

 of this mixture give: 



When plated immediately, no plaques, or less than 100 ultramicrobes 

 per cubic centimeter. Thus, the filtrate contained less than 1,000 per cc. 



After one and one-quarter hours the plating shows no plaques. 



After two and one-half hours there are 9 plaques, or 900 ultramicrobes 

 per cubic centimeter. 



After three and three-quarter hours, in a 1:10 dilution, there are 27 

 plaques, or 27,000 per cubic centimeter. 



After five hours, a 1:1000 dilution shows 13 plaques, representing 

 1,300,000 per cubic centimeter. 



In this last experiment (B) the ultramicrobes were present in 

 the filtrate in very small numbers, certainly less than 1000 per 

 cubic centimeter, that is, there were less than one-sixteenth as 

 many as in the filtrate of the first preparation (A). Nevertheless, 

 the suspension was completely lysed in ten hours and the fluid 

 remained sterile indefinitely. 



It should be noted that the multiplication of the ultramicrobes 

 was much more rapid in the second experiment than in the first, 

 and that this corresponds exactly with the idea of a greater viru- 

 lence. These experiments show also that the number of ultrami- 

 crobes inoculated is without effect upon the intensity of the phenom- 

 enon, but that the important thing is the quality of the bacterio- 

 phage, that is, its virulence. 



It is significant that the two strains of bacteriophage under 

 discussion were derived from the same patient, but were taken 

 at an interval of twenty-four hours. It is the same bacteriophage 

 whose virulence has been increased in vivo. 



It would be possible to cite a great number of experiments of the 

 same order. On each page of this text facts will be found that 

 show that the essence of the phenomenon is the virulence of the 

 bacteriophage, a virulence extremely variable, exalted, or at- 

 tenuated, or indeed absent for a given bacterium according to the 

 conditions at the moment obtaining. This extreme variability 

 observed especially in vivo is due to a variety of conditions. It is 

 less in vitro, where we are able, within certain limits, to secure a 

 relative stability. 



