298 TUBERCULOSIS 



their appearance round the sites of tuberculin inoculation, 

 generally within a few hours, and at the end of twenty-four 

 hours there is a distinct inflammatory papule about half an inch 

 in diameter, with a somewhat paler centre like a spot of urticaria ; 

 sometimes in the centre there are minute vesicles. The maximum 

 effect usually occurs within forty-eight hours, and after that time 

 the reaction gradually recedes. Such is the typical reaction, but 

 of course slighter, and also more intense reactions are met with. 

 In a negative reaction all three points of scarification show 

 merely a slight traumatic redness which soon passes off. 



For the ophthalmo-reaction Calmette uses a purified tuberculin. 

 The tuberculin is prepared as in Koch's original method, and is 

 precipitated with 95 per cent, alcohol ; the precipitate is then 

 dissolved in water. This process is repeated other two times, 

 and the final precipitate is made up as a 1 per cent, solution in 

 distilled water. For use, in the case of an adult, a drop of this 

 solution is placed in the conjunct! val sac and the fluid allowed 

 to spread over the surface ; for children about half this quantity 

 is sufficient. In the case of a positive reaction the ocular con- 

 junctiva is congested, the lids become somewhat swollen and 

 their inner surface presents a bright red colour, there is increased 

 secretion of tears and a varying amount of fibrinous exudation. 

 The reaction usually reaches its maximum in from six to ten 

 hours after the instillation, and commences to pass off in from 

 twenty-four to thirty-six hours, in children a little sooner. 



The general results obtained by these two reactions appear to 

 correspond closely. A distinct positive result obtained by either 

 is practically conclusive as to the presence of a tubercular lesion. 

 In cases of latent tuberculosis the reaction is sometimes obtained, 

 sometimes not. Again, in very advanced cases of tuberculosis, 

 especially a short time before death, a negative result may be 

 got ; in some of these cases v. Pirquet has met with a colourless 

 papule or a livid spot without exudation, conditions which he 

 describes as indicating a " cachectic reaction." The ophthalmo- 

 reaction is the more easily applied, at least in adults, but its use 

 is contra-indicated when there is any abnormal condition of the 

 conjunctiva. Even apart from this, however, inflammatory 

 symptoms of disagreeable severity sometimes supervene. It 

 should also be noted that a second test ought not to be applied 

 to the same eye, as the first may produce a condition of super- 

 sensibility (p. 297). v. Pirquet claims for his method that in 

 the case of children it can be satisfactorily carried out with 

 greater ease than the ophthalmic test. 



It will be recognised that the processes underlying the original 



