ALLERGIC REACTIONS 335 



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, coeteris 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 ordi- 

 narily 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 ceached 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. 



The great advantage of v. Pirquet's method as compared with 

 the older subcutaneous method of Koch is, of course, its simplicity, 

 and the fact that undesirable systemic effects hardly ever occur, 

 providing that the abrasion has been made lege artis, and that 

 opportunity for undue absorption has not been afforded. As in the 

 case of the subcutaneous method, however, a positive reaction 

 merely denotes the presence of a tubercular focus somewhere in the 

 body, which need not be active, however, and the diagnostic value 

 of the method is hence limited to the same extent and even more. 

 The greatest sphere of usefulness indeed seems to lie in its application 

 to the diagnosis of tuberculosis in very young children. From a 

 study of 757 children in which the test had been applied by v. Pirquet 



