ALLERGIC REACTIONS 315 



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 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. 



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, provid- 

 ing 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 

 and in which the results were compared with the clinical findings, 

 it appears that of the clinically tubercular cases 87 per cent, 

 gave the reaction, while this was also found in 20 per cent, of 

 the non-suspected cases. The negatively reacting tubercular cases, 

 v. Pirquet points out, were almost exclusively cachectic or in the 

 last stages of miliary tuberculosis. 



As the result of a study of 124 children which had come to autopsy 

 and in which the test had been made, v. Pirquet concludes that a 



