212 ACTIVE IMMUNIZATION 



(a) When a series of measurements of the opsonic power of the 

 blood reveals a persistingly low opsonic power with respect to the 

 tubercle bacillus, it may be inferred, in the cases where there is 

 evidence of a localized bacterial infection which suggests tuber- 

 culosis, that the infection in question is tuberculous in character. 



(b) When repeated examination reveals a persistingly normal 

 opsonic power with respect to the tubercle bacillus, the diagnosis 

 of tubercle may with probability be excluded. 



(c) W 7 hen 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 derived at where we have at disposal 

 the result of an isolated blood examination : 



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

 culo-opsonic 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. 



(6) When an isolated blood examination reveals that the tuberculo- 

 opsonic 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) When the tuberculo-opsonic 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 incit- 

 ing 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 tuber- 

 culous 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 



