SCIENCE IN MEDICINE 251 



of the bacteria, and by counting, say, fifty consecutive poly- 

 morphonuclear neutrophils, and at the same time the number 

 of bacteria ingested by those cells, it is possible to work out 

 the average number of bacteria ingested per cell. We will 

 suppose that in the first film — that is, the one obtained after 

 using normal serum — this average works out at 9/5 bacteria 

 per cell, and that in the second film, obtained with the patient's 

 serum, it is only 8*5 per cell. 



Then in this case the patient's serum has not such a high 

 opsonic power as that of the normal serum. Taking the normal 

 " index " as unity, and comparing the patient's average with the 

 normal average, the patient's opsonic " index " is in this case o'89. 



Thus: Normal serum = 9"5. As for purposes of comparison 

 normal serum is always taken as unity, then in the same 



ratio patient's serum = — =o - 89. This is spoken of as the 



patient's opsonic index, and it can be taken as a guide as to 

 the richness of his blood in these protective substances. 



Having inquired into the nature of opsonins as regards the 

 part played by them in immunity, and having briefly reviewed 

 the method employed for their detection and measurement, it 

 is necessary to consider the class of cases in which therapeutic 

 inoculation is applicable. For this purpose the classification 

 suggested by Wright is the most convenient : 



(1) Localised bacterial infections. 



(2) Localised infections associated with constitutional dis- 

 turbance. 



(3) Septicaemias. 



Class 1. — In the case of localised infections the bacteria have 

 found a suitable soil for growth ; and it may be taken generally 

 that the less well supplied with blood any particular part of 

 the body is the more likely is it to be a favourite site for 

 infection. In these cases, therefore, therapeutic inoculation 

 offers the best chance of success. Auto-inoculation is hardly 

 taking place at all, and in most cases there is nothing to prevent 

 the elaboration of enough protective substances, in response to 

 vaccination, to cure the disease. Carbuncles, boils, etc., rapidly 

 disappear under this treatment. Early pulmonary tuberculosis 

 should probably be included under this category, and it is very 

 likely that in such cases treatment with a tubercle vaccine would 

 be rewarded with great success. 



