BACTERIAL VACCINES 281 



asserts that in healthy individuals the range should be not 

 more than from 0.8 to 1.2, and that an index below 0.8 may 

 show a great susceptibiUty for the organism tested, infection 

 with the given organism if derived from the individual, or 

 improper dosage in case attempts have been made to im- 

 munize by using killed cultures, vaccines, of the organism. 



On the occasion of the author's visit to Wright's clinic 

 (1911) he stated that he used the determination of the 

 opsonic index chiefly as a guide to the dosage in the use of 

 vaccines. 



Most workers outside the Wright school have failed to 

 recognize any essential value of determinations of the 

 opsonic index in the use of vaccines. Some of the reasons 

 for this are as follows: The limit of error in phagocytic 

 counts may be as great as 50 per cent in different series of 

 fifty, hence several hundred must be counted, which adds 

 greatly to the tediousness and time involved; the variation 

 in apparently healthy individuals is frequently great, hence 

 the ''normal" is too uncertain; finally the opsonic index 

 and the clinical course of the disease do not by any means 

 run parallel. Undoubtedly the method has decided value 

 in the hands of an individual who makes opsonic deter- 

 minations his chief w^ork, as Wright's assistants do, but it 

 can scarcely be maintained at the present time that such 

 determinations are necessary in vaccine therapy. Never- 

 theless that opsonins actually exist and that they play an 

 essential part in phagocytosis, and hence in immunity, is 

 now generally recognized. 



BACTERIAL VACCINES. 



Whether determinations of opsonic index are useful or 

 not is largely a matter of individual opinion, but there is 

 scarcely room to doubt that Wright has conferred a lasting 

 benefit by his revival of the use of dead cultures of bacteria, 

 bacterial vaccines, both for protective inoculation and for 

 treatment. It is perhaps better to use the older terms 

 "vaccination" and "vaccine" (though the cow, vacca, is 

 not concerned) than to use Wright's term "opsonic method" 



