DIAGNOSIS. 601 



Babes supposed that the increased susceptibility 

 of tuberculous persons was due to a summation 

 of effects of the products of the tubercle bacilli 

 in the tuberculous focus and the injected tuber- 

 culin. Von Pirquet and Schick explain the tuber- 

 culin reaction as a phenomenon of allergy. This 

 explanation is the most satisfactory one. (See 

 Allergy.) 



In view of ^aegeli's finding of tuberculosis, ^imitations 

 healed or active, in 97 per cent, of autopsies, the i5e l oi sn 

 value of the tuberculin reaction would seem to be Tuberculin - 

 a relative one, and that the number of positive 

 reactions obtained would depend on the amount of 

 tuberculin used. 



Experience has taught certain limitations to the 

 diagnostic value of tuberculin: 1. The test can 

 not be applied to febrile cases inasmuch as the 

 pre-existing fever could not be separated from that 

 which the tuberculin might produce. 2. Cases of 

 advanced tuberculosis frequently fail to give the 

 reaction. The tissues of such patients have be- 

 come resistant to the poison. 3. It is said that 

 tuberculin frequently causes a similar reaction in 

 those suffering from leprosy, actinomycosis and 

 syphilis. Cornet and Meyer suggest that the 

 phenomenon as it occurs in leprosy and actinomy- 

 cosis is to be considered in the nature of a "group 

 reaction" in view of the close relationship of the 

 tubercle bacillus to actinomyces and Bacillus leprce. 

 It does not always occur in syphilis, and in posi- 

 tive cases a latent tuberculosis may be responsible 

 for the reaction. By a number of writers the facts 

 just stated are taken to indicate that the reaction is 

 not of specific character; that it may often be ob- 

 tained in the tuberculous by the injection of ap- 



