ESTIMATION OF THE OPSONIC CONTENT OF THE BLOOD 213 



degree of immunity which develops as the result of bacterial vacci- 

 nation (which see) he advocated that the dosage and frequency of 

 injection should be controlled by opsonic determinations. Accord- 

 ing to his teachings the injection of a dose of vaccine is followed 

 by a decrease of the opsonins (negative phase), which is of variable 

 degree and duration, according to the amount injected. This is 

 followed by an increase (positive phase) coincidently with which 

 there is a corresponding improvement in the patient's condition. 

 The idea of proper vaccination, then, is to so gauge and interspace 

 the different doses that a negative phase is obviated as far as possible 

 and a "high tide" of increased opsonic content secured. 



It would lead too far to discuss the teachings of Wright in any 

 detail at this place; suffice it to say that nearly all investigators 

 who have busied themselves with his technique have come to the 

 conclusion that the unavoidable errors are such that accurate results 

 cannot be obtained. As a consequence its application looses much 

 of its raison d'etre, and at the present time there are few outside of 

 Wright's own circle who are influenced in either diagnosis or treat- 

 ment by the opsonic index. But this failure does not in the least 

 diminish the importance of the principle of bacterial vaccination, 

 a principle which had, however, been firmly established long before 

 the opsonins were discovered. 



It would, of course, be most desirable to possess an index to 

 dosage and frequency of injection in vaccination, but a consideration 

 of what has already been said regarding the aggressive forces of 

 the bacteria will at once suggest that even if it could be possible 

 to estimate the "opsonic index" with accuracy, this alone would 

 scarcely be of much value in the treatment of infections. For 

 unless we can influence the aggressive forces of the invading organ- 

 isms and notably their capsule-forming power, the production of a 

 high content of opsonins in itself would lead to nothing. 



In conclusion, I would briefly call attention to the fact that in 

 the early days of the opsonic "high tide" I advocated a different 

 method of estimating the opsonins, which was based upon the prin- 

 ciple of dilution, and I note with satisfaction that this principle is 

 now utilized in practically all laboratories (outside of Wright's) in 

 which opsonic studies are being carried on. 



