ESTIMATION OF THE OPSONIC POWER OF THE BLOOD 2O/ 



When spontaneous cure takes place it is accompanied by, 

 and is apparently due to, an increase of the opsonic power 

 of the blood. Thus, in pneumonia the opsonic index tested 

 with pneumococci is below normal until the crisis is reached, 

 when there is a sudden rise above normal, so that the patient 

 is for a short period more resistant than the healthy person. 

 In staphylococcic lesions the rise is as a rule more gradual 

 and irregular, and the lesions may persist when the index is 

 high, though in most cases this heralds a rapid improvement. 



The behaviour of the opsonic index in tuberculosis is very 

 interesting. The main feature is that it is very variable, 

 especially in patients in whom the disease is progressing 

 rapidly and in those who are taking exercise. This 

 variability is supposed to be due to auto-inoculation, bacilli 

 being detached from the lesions and lodged in the tissues, 

 where they act as small doses of vaccine. As a general rule 

 it is thought that (in lupus especially) a high index is of 

 favourable import, and vice versa, but there is not the same 

 more or less direct relation between a high index and the 

 process of cure that there is in pneumococcic and some other 

 infective processes. A patient may die of tuberculosis whilst 

 his opsonic index is high. This seems paradoxical, but the 

 conditions are exceedingly complex, and the symptoms of 

 pulmonary tuberculosis are due almost as much to the other 

 organisms (streptococci, etc.) as to the tubercle bacilli itself. 

 In miliary tuberculosis the index is often high, and shows 

 great variations in a short time. I believe you are almost 

 safe in diagnosing tubercle if the index is below o - 8 or above 

 1-2, and if it shows marked variations from day to day the 

 probability is still greater. 



A low opsonic index towards a given organism, therefore, 

 denotes either (i) an infection with that organism, or (2) a 

 low power of resistance, so that if the patient is exposed to 

 infection invasion will readily take place. In such cases he 

 should be carefully shielded from exposure, and the general 

 health improved by fresh air, careful feeding, tonics, etc. 



A high opsonic index (i.e., one decidedly above normal) 

 usually indicates that the patient has had an attack of the 

 disease caused by the organism in question, and has over- 

 come it. Normal persons differ very little amongst them- 

 selves; for instance, in a series of healthy persons, if the 



