ALLERGIC REACTIONS 291 



reveal the existence of a distinct brown scab measuring about 1 mm. 

 in diameter, both at the point of inoculation as well as at that of 

 control, the abrasion has been too slight, and the test must be 

 repeated. 



The appearance of a positive reaction when fully developed is 

 well shown in Plate VII, and contrasts markedly with that of the 

 control. If the abrasions are examined at frequent intervals it will 

 be observed that a small wheal appears within a few minutes both 

 at the control and the test point which soon becomes surrounded 

 by a pink halo. This disappears after a few hours, leaving a small 

 red area, in the centre of which a tiny scab begins to form. At 

 the control point the redness is still discernible after twenty-four 

 hours, but then fades away. At the test point, in positive cases, 

 the red area begins to increase in size after a period of time which 

 varies between three hours and several days. Coincidently the 

 inflammatory area becomes elevated (papular) and develops rapidly 

 in size. At the end of forty-eight hours the reaction has usually 

 reached its height. At this time the diameter of the "papule" will 

 average about 10 mm., but it may be much larger up to 30 mm., 

 the size, cceteris paribus, depending upon the quantity of tuberculin 

 which has been absorbed. The centre of the papule is sometimes 

 pale, like an urticarial wheal. The surface otherwise is frequently 

 finely vesiculated; pustulation, however, never occurs. While ordin- 

 arily the entire area is intensely hyperemic, nearly colorless papules 

 are sometimes seen in very advanced cases of tuberculosis, at a 

 time when the power of reaction on the part of the individual has 

 almost disappeared (cachectic reactions). The hyperemic area is 

 usually limited to the papule itself, but occasionally extends beyond, 

 forming an areola, which strongly reminds one of what is seen in 

 cases of vaccination. 



After having reached its height the exudation gradually subsides 

 The swelling disappears in from five to eight days, but the pigmen- 

 tation which then develops frequently remains visible for a number 

 of weeks. 



Exceptionally the reaction does not begin to develop until after 

 twenty-four hours following the inoculation. Such a delayed 

 response v. Pirquet speaks of as a torpid reaction. This is notably 

 seen in individuals who show no clinical evidence of tuberculosis, and 

 is the more frequent the older the patient. 



