ESTIMATION OF BACTERICIDAL SUBSTANCES 73 



diluted in the proportion of 1 to 100,000 and 5 c.c. of the resultant 

 dilution distributed over the surface of plates. The number of 

 developing colonies is then counted. The result shows the following: 



5 c.c. of a 1 to 100,000 1 c.c. of the undiluted emulsion 



Type. dilution contain: hence contains: 



Cholera vibrios .... Plate I 20.0 organisms 



Plate II 21.0 organisms 



Average 21.5 organisms 410,000 organisms 



Typhoid bacilli .... Plate I 21.0 organisms 



Plate II 30.0 organisms 



Average 25.5 organisms 510,000 organisms 



B. Estimation of the Bactericidal Strength of the Serum. Equal 

 quantities (1 c.c.) of the undiluted serum and of various dilutions 

 of the original emulsion are mixed and after twenty-four hours' 

 exposure plated out, when the number of developing colonies is 

 counted. 



Dilution of the Number of 

 bacterial developing 



Type. emulsion. colonies. 1 c.c. of serum thus kills: 



Cholera undiluted 1 



1 to 10 



1 to 100 About 410,000 organisms 



1 to 1000 



1 to 10000 



1 to 100000 



Typhoid 1 to 10 8 



1 to 100 1 



1 to 1000 About 5100 organisms 



1 to 10000 



1 to 100000 



A good idea of the progress of bacteriolysis, and the gradual gain 

 of reproduction over destruction, when the amount of serum was 

 insufficient at the start to kill all the organisms, as also of the 

 differing resistance which different strains of organisms offer to the 

 destructive forces of the serum, may be had from the study of the 

 following table (taken from Trommsdorff). The figures in general 

 represent the variations noted in different tests; those of the a 

 series were obtained with a typhoid strain that had been freshly 



