292 IMMUNOLOGICAL METHODS OF DIAGNOSIS 



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 con- 

 cludes that a positive cutaneous reaction is never observed in 

 the absence of a tubercular lesion, that a negative reaction 

 ordinarily indicates freedom from tuberculosis, but that such 

 a result may also be obtained in the last stages of the disease. 

 As a positive reaction may be expected in over 90 per cent, of all 

 individuals after the fourteenth year,. it is clear, however, that the 

 diagnostic significance of the reaction is then practically nil. As 

 35 per cent, of all children, moreover, give a positive cutaneous 

 reaction between the ages of six and ten already, it is evident that 

 even at this age the diagnostic value of the reaction is limited. 



The Tuberculin Test According to Calmette (conjunctival method). 

 While Calmette advocates the use of a tuberculin which essentially 

 contains the alcohol-insoluble constituents of bovine tubercle bacilli, 

 made up into a \ per cent, aqueous solution, one may also 

 employ a 5 per cent, solution of the old tuberculin of Koch. One 

 or two drops of either solution are placed upon the conjunctiva of 

 one eye near its inner canthus, when the lids are held together for 

 about a minute. In the normal individual slight redness may then 

 develop and persist for a few hours, after which it disappears. In 



