382 TUBERCULOSIS 



cases definitely tuberculous. A positive reaction is here of more 

 value than a negative one. 



Calmette's reaction was introduced soon after Von Pirquet's, and 

 consists in a slight conjunctivitis and oedema of the caruncle, with 

 sero-fibrinous discharge, which occurs in tuberculous subjects after 

 the instillation of a drop of well-diluted tuberculin into the eye. 

 Since glycerin has an irritant action, a special preparation devoid 

 of this substance is sold for the test. It is put up in a dry form 

 (being precipitated by alcohol), and when dissolved in water 

 according to the instructions gives a dilution corresponding to 

 i : 100 or i : 200 of the original tuberculin. The strength has 

 been gradually decreased owing to calamitous results having been 

 obtained when the stronger dilutions were used. It should 

 certainly never be used when the eyes are affected, and even 

 when they are healthy I personally do not consider the risk worth 

 running unless the diagnosis is of great importance, and all other 

 methods have been tried and have failed. 



2. The Opsonic Index. Numerous observations by different 

 observers have shown that in health the opsonic index to tubercle 

 lies between 0-8 and 1*2, the exceptions being very rare and due 

 perhaps to slips in the technique. As a matter of fact, these are 

 outside figures, and in the great majority of cases the index will 

 be found to lie between 0*95 and 1*05. If, therefore, the diagnosis 

 lies between health and tubercle, an index below 0-8 or above 1-2 

 is very strong evidence in favour of the latter, becoming more 

 convincing the remoter it is from these figures, either above or 

 below. Indices between 0*8 and 1*2 are not of much value, yet a 

 figure of, say, 0-85 on several occasions is very suggestive. 



There is not sufficient evidence as yet to show how other 

 diseases influence the tuberculo-opsonic index. In the majority 

 of cases the figures lie within the normal limits, but there are 

 occasional exceptions. In general, therefore, the results given 

 above will apply, but the conclusions are less certain. 



A rapid variation of the index, either (a) spontaneous, or 

 apparently so, or (b) due to auto-inoculation from exercise or 

 massage of the lesion, or (c] caused by an injection of a small 

 dose of tuberculin, is much more suggestive indeed, practically 

 diagnostic, supposing no errors are made in the determination. 

 And it must be emphasized that when the opsonic index is 

 required for diagnostic purposes, the most careful technique and 

 attention to every detail is absolutely necessary. 



