OPSONIC INDEX AND VACCINE THERAPY 333 



pham 8 depends upon a combination of the dilution method and a 

 modification in the method of counting. They make comparative 

 tests of the same serum, diluted from 1 to ten to 1 to one hundred in 

 salt solution, and estimate the opsonic power, not by determining 

 the average number of bacteria to the leukocyte, but by taking a per- 

 centage of the total number of leukocytes which take part in the 

 phagocytosis, that is, contain any leukocytes at all. The bacterial 

 emulsion for this method should be so thin that, in normal serum, 

 only about 50 per cent, of the leukocytes will contain bacteria. 



That Wright's method, or any of the others, gives absolutely 

 accurate results will hardly be claimed by any one who has worked 

 upon opsonic-index estimations. There are certain uncontrollable 

 variable factors, some of which have been pointed out above; and, 

 apart from these, the delicacy of the technique is such that reliable 

 results can ordinarily be 'obtained only by trained workers after con- 

 siderable practice and experience. Even in such hands the per- 

 centage of personal error is more likely to be above than below 10 

 per cent. For ordinary clinical purposes, therefore, in the control 

 of cases the estimation of the opsonic index is not often practicable. 



On the other hand, there can be little doubt about the fact that 

 careful comparative estimation, by Wright's method and by some 

 of the modifications, carried out by workers with experimental train- 

 ing and consequent attention to extensive controls, have yielded 

 results of sufficient accuracy to permit the recognition of definite 

 facts concerning opsonins. It is beyond question, therefore, that the 

 conclusion regarding the relation of opsonic fluctuations to clinical 

 conditions and the general significance of opsonins emanating from 

 laboratories like those of Wright, E~eufeld, Hektoen, and some others 

 may be accepted as fact especially since in most essentials such 

 workers have agreed. In consequence we are now in possession of 

 knowledge regarding the opsonic constituents of the blood in health 

 and disease, and in the course of active immunization with bacterial 

 vaccines, which is of the greatest practical importance. We may 

 summarize the results of such investigations by saying that in many 

 of the infections of man the resistance of the patient is roughly pro- 

 portionate to the opsonic index and that properly spaced inocula- 

 tion with suitable quantities of dead bacteria (vaccines) will raise 

 the opsonic index and lead to recovery in many of the localized 

 subacute and chronic conditions. 



As to the usefulness of the treatment in various infections and 

 the limitations within which we may hope for results opinions differ, 

 and these will be discussed more fully below. Before we proceed 

 to this, however, it will be useful to consider the studies upon which 



8 Simon and Lamar. Johns Hop. Hosp. Bull, Vol. 17, 1906; Simon, 

 Lamar, and Bispham, Jour. Exp. Med., Vol. 8, 1906 ; Simon, Jour. A. M. A., 

 Vol. 48, 1907, p. 139. 



