ESTIMATION OF THE OPSONIC POWER OF THE BLOOD 155 



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 tuber- 

 culosis are due almost as much to the other organisms (strepto- 

 cocci, 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 0-8 or above i-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 care- 

 fully 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 overcome it. Normal 

 persons differ very little amongst themselves ; for instance, in a 

 series of healthy persons, if the average index be taken as normal, 

 it is unusual to find one below 0-95 or above 1-05. 



A study of the opsonic index is the basis of Wright's method 

 of treatment by means of vaccines. In carrying this out the 

 patient's opsonic index is raised by injections of the organisms 

 which cause the disease (carefully sterilized) in appropriate doses. 

 These are given in a healthy part of the body, where the tissues 

 are stimulated to produce opsonins against the organisms intro- 

 duced, and these opsonins are carried in the blood to the lesion. 

 The reason why it is necessary to estimate the opsonic index of 

 the blood from time to time in carrying out this process is that 

 the injection causes it to fall for a variable time (usually a few 

 days — the negative phase), and if a second injection be given 

 before this fall has gone off and been succeeded by a rise above 

 the initial level, harm rather than good will follow. 



The method of preparing these vaccines is roughly as follows : 

 The cultures should in all cases where practicable be prepared 

 from the organisms isolated from the patient himself. "Stock" 

 vaccines may do good in some cases, especially, perhaps, in 

 staphylococcic diseases ; but in diseases due to streptococci, B. coli, 

 etc., they are not nearly so likely to succeed as vaccines specially 

 prepared : these organisms differ slightly in different cultures, and 



