182 APPLIED IMMUNOLOGY 



centimetres in diameter. The intensity of the reaction 

 varies from a hyper^emia with papule formation to 

 many papules on an oedematous and inflamed base, 

 to a markedly indurated zone exuding serum from the 

 scarification site ( Plate III ) . The inflamed area may 

 persist for a week or two. The reaction is not at- 

 tended with general fever or other symptoms. A 

 positive test simply indicates the presence of tuber- 

 culosis; it does not specify, as does the focal reaction 

 in the subcutaneous test, that a suspected joint, cor- 

 nea, epididymis, prostate, etc., is tuberculous. A pa- 

 tient with tuberculous peribronchial lymphadenitis 

 may exhibit a positive reaction, while his particular 

 cause for complaint, a troublesome knee, may be 

 gonorrhoeal. 



Detre had evolved a modification of the above, 

 known as a differential tuherculin test and therapeutic 

 control. It has for its objects the difl'erentiation of 

 the human and bovine types of infection, the measure- 

 ment of the extent of the disease, whether incipient or 

 advanced, the selection of the best variety of tuber- 

 culin for immunization and a control in therapy 

 superior to the opsonic index. Three varieties of tuber- 

 culin are employed: Koch's " O. T.," " B. F." prepared 

 from bacilli of the human type, and " B. F." as in the 

 von Pirquet method, preferably the flexor surface of 

 the forearm is cleansed with ether and a pledget of 



