ESTIMATION OF THE OP SONIC CONTENT OF THE BLOOD 219 



that with the patient's serum the average number of organisms per 

 cell was 5 and with the normal serum 10; then from the equation 

 10 : 1 : : 5 : x, it would follow that the opsonic index is 0.5. 



When Wright's studies on the opsonins first appeared they 

 attracted a great amount of attention. This was largely owing to the 

 fact that the author attached a significance to his observations 

 which, if justified, would have meant an enormous advance not 

 only in the diagnosis of certain bacterial infections, but also in their 

 treatment. I cite some of his more important diagnostic deductions : 



1. Conclusions which can be arrived at when we have at 

 disposal the results of a series of measurements (opsonic determi- 

 nations) : 



(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 in which there is 

 evidence of a localized bacterial infection which suggests tuber- 

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



(6) When repeated examination reveals a persistently normal 

 opsonic power with respect to the tubercle bacillus, the diagnosis 

 of tubercles may with probability be excluded. 



(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 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-opsbnic 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. 



