﻿432 STRONG. 



tions are sometimes encountered in the immunization of inonkeys, but 

 they are less variable in the other lower animals. 



Lamb and Forster 29 have proposed to adopt Wright's method of 

 standardizing typhoid vaccine by determining the amount of the vaccine 

 which will completely neutralize or remove the amboceptor content of 

 a fixed quantity of normal goat's serum. However, since the binding 

 power in vitro of the receptors in the vaccine, for the amboceptors 

 of the serum may perhaps not exactly represent the immunizing power 

 of the vaccine in the animal body, we have preferred to employ the 

 method I have described. This method of standardization of the pro- 

 phylactic by the units of immunity it gives rise to is obviously not 

 an accurate one, but it is sufficiently accurate for all practical pur- 

 poses. In standardizing our smallpox vaccine we regard the reaction 

 obtained in a monkey following inoculation with it as the most import- 

 ant test of its efficacy; the exact degree of the reaction (which varies 

 with the natural variation in the immunit} r of the animals) is not so 

 important so long as a distinct reaction is obtained. In standardizing 

 our cholera prophylactic we also seek to obtain a certain reaction in the 

 serum of the rabbit, following its inoculation. The exact degree of the 

 reaction obtained, provided a certain limit has been reached, is obviously 

 of less importance, for the reason already given. 



IMMUNIZING POWER AND VIRULENCE OF THE ORGANISM. 



Another point about which some further discussion seems necessary 

 is that of the immunizing power of the cholera organism to be chosen 

 for the preparation of the prophylactic. 



Pfeiffer, Friedberger 30 and 1 31 found that, with cholera spirilla, a 

 greater immunity was obtained with the more virulent organism. 

 Pfeiffer and Friedberger employed four strains in their investigations. 

 My experiments were carried on with two strains of cholera spirilla of 

 widely different virulence and I was able conclusively to show that the 

 virulent organism, upon inoculation, produced a higher immunity and 

 at the same time bound a greater number of amboceptors in a cholera 

 immune serum than did the avirulent one. At the time of the publica- 

 tion of these experiments I stated that "these conclusions apply to the two 

 strains of cholera spirilla employed in the foregoing experiments. 

 Whether they will also hold good with other strains of this spirillum or 

 for micro-organisms in general must be decided by further experimental 

 work." The experiments of Meinicke, Jaffe and Flemming seem con- 

 clusively to show that with different strains of the cholera spirillum 



20 Sclent. Mem. Med. and San. Off., India, Calcutta (1906). 21, 7. 

 =° Berl. Klin Wchnsch. (1902), 39, 581. 



31 Publications of the Bureau of Government Laboratories, Biological Labora- 

 tory. Manila (1904), 21, 1, and J. Exp. Med. (1905), 7, 229. 



