226 ACTIVE IMMUNIZATION 



(c) When there is revealed by a series of blood examinations a 

 constantly fluctuating opsonic index the presence of active tuber- 

 culosis may be inferred. 



2. Conclusions which may be arrived at where we have at disposal 

 the result of an isolated blood examination: 



(a) When an isolated blood examination reveals that the tuber- 

 culoopsonic power of the blood is low, we may according as we 

 have evidence of a localized bacterial infection or of constitutional 

 disturbance infer with probability that we are dealing with tuber- 

 culosis in the former case with a localized tuberculous infection, 

 and in the latter with an active systemic infection. 



(b) When an isolated blood examination reveals that the tuber- 

 culoopsonic power of the blood is high, we may infer that we have to 

 deal with a systemic tuberculous infection which is active, or has 

 recently been active. 



(c) W T hen the tuberculoopsonic power is found normal or nearly 

 normal, while there are symptoms which suggest tuberculosis, we 

 are not warranted, apart from the further test described below, in 

 arriving at a positive or a negative diagnosis. 



The further criterion to which reference has been made in the 

 preceding paragraph is the following: 



When a serum is found to retain in any considerable measure, 

 after it has been heated to 60 C. for ten minutes, its power of 

 inciting phagocytosis, we may conclude that "incitor elements" 

 (immune opsonins) have been elaborated in the organism either in 

 response to auto-inoculations, occurring spontaneously in the course 

 of tuberculous infection, or, as the case may be, under the artificial 

 stimulus supplied by the inoculation of tubercle vaccine. 



The above considerations apply also in the case of other bacterial 

 infections, and in the examination of exudates as well. 



As Wright regarded the opsonic index as an indicator of the 

 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. 



