SPECIFICITY OF TUBERCULIN REACTION. 51 



This test is much milder and more agreeable to the patient than the sub- 

 cutaneous one, and in ambulatory work more significant, inasmuch as it does 

 away with any necessity for considering as a guide the temperature taken 

 by the untrained and usually unreliable patient. 



The ophihalmo reaction is contraindicated in all diseases of 



Contraindi- ^6 eye, tuberculous or otherwise. If one eye only is affected, 



cations for the the reaction should not be undertaken upon the healthy eye. 



Ophthalmo Similarly, patients who have had some eye disease, even though 



Reaction. man y years ago, those who by reason of their occupation are 



readily exposed to eye diseases, or who live in districts where 



trachoma is prevalent should be excluded from the test. The reason being 



that in those individuals the conjunctival mucous membrane becomes a 



locus minoris resistentiae and therefore easily inflamed 



Repeated instillations of tuberculin into the same eye, may set up very 

 severe disturbances. Scrofulous children often show reactions of the third 

 degree, inasmuch as they possess the constitutional tendency which makes 

 them easily susceptible to conjunctivitis or phlyctenulae. In patients with 

 a positive ophthalmo reaction which has subsided, a recurrence of the con- 

 junctival inflammation is frequently observed when they begin to receive 

 subcutaneous inoculations of tuberculin for therapeutic or even diagnostic 

 purposes. 



The Specificity of the Tuberculin Reaction. 



The one real essential for the practical application of all biological reactions, is 

 the specificity of the same. There is, however, as will be repeatedly pointed out 

 further on, no single absolutely specific reaction. In fact, it would be more exact to con- 

 sider these biological reactions only relatively specific; the latter depending upon the 

 quantity of the required antigen and the reacting organism. In this connection it 

 may also be said, that it is never possible to draw an exact line between the specific and 

 non-specific biological reactions. There always will be a doubtful zone. As a general 

 rule, however, it may be said that the smaller the quantity of antigen that is required 

 and the stronger the resulting reaction, the more probable is the biological specificity. 



In tuberculosis this problem is rendered still more complex by the 

 pathological anatomical findings, whereby it is shown that an extraordinary 

 high percentage of individuals have undergone tubercular infection at some 

 time during life. The clinical consideration of tuberculosis, however, does 

 not deal with the diagnosis of these harmless, practically healed tuberculous 

 foci; what the clinician desires to know is whether or not a group of symptoms 

 manifested in a patient is of a tuberculous nature or not. In other words, 

 it is not the latent, inactive, but the active form of tuberculosis that is to be 

 diagnosed. If, therefore, one views the various tuberculin tests from such a 

 stand-point as this, he arrives at very material differences. 



The reaction of least specificity in adults is the v. Pirquefs cutaneous 

 reaction. In children it is far more specific. 



