VIRULENCE OF THE BACTERIOPHAGE 153 



Plating of dilution 10~^; bacterial layer smooth, with 141 small 



plaques. 

 Plating of dilution 10~^; layer with 13 plaques (diameter about 



0.25 mm.). 

 Plating of dilution 10~^; normal culture without plaques. 

 Platings of dilutions 10~^ and 10~^; normal culture without plaques. 

 Computation upon the basis of the above would indicate that the 

 original suspension contained 26,000,000 corpuscles per cubic centi- 

 meter.* 



Bacteriophage No. 2. 



Plating of dilution 10~^; isolated colonies. 



Plating of dilution 10"^; scattered traces of growth with isolated 



colonies in the open spaces. 

 Plating of dilution 10~^; the same, except that the fragments of 



culture are somewhat more extensive. 

 Plating of dilution 10~^; the same, still more culture evident. 

 Plating of dilution 10^^; culture layer with numerous plaques. 

 Plating of dilution 10""; 27 plaques (diameter, 3 mm.). 

 Plating of dilution lO"'^; 3 plaques. 

 Plating of dilution 10~^; 1 plaque. 



Plating of dilution 10~^; normal culture without plaques. 

 Plating of dilution 10"^°; normal culture without plaques. 

 The original suspension of bacteriophage No. 2 contained therefore, 

 540,000,000 corpuscles per cubic centimeter. 

 Bacteriophage No. 3. 

 Platings of dilutions 10~^ to 10~^; plates sterile. 

 Platings of dilutions lO""* and 10~^; traces of culture. 

 Plating of dilution lO"**; confluent plaques. 

 Plating of dilution 10~^; 38 plaques (7 mm. in diameter). 

 Plating of dilution 10~^; 5 plaques. 



Platings of dilutions 10~^ and lO^^"; normal culture without plaques. 

 The original suspension of this race contained, then, 7,600,000,000 

 corpuscles per cubic centimeter. 



The number of corpuscles in the three suspensions being respectively 

 26, 540, and 7600 million per cubic centimeter after bacteriophagy has 

 continued in identical suspensions for the same length of time obviously 

 means that these figures represent the power of multiplication of the 



* 0.05 cc. of dilution 10~^ containing 13 corpuscles, 1 cc. would contain 20 times 

 as many, or 260. The original suspension would then contain 260 X 10^ = 

 26,000,000. 



