316 IMMUNOLOGICAL METHODS OF DIAGNOSIS 



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 its diagnostic value 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 J 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 the tuber- 

 cular subject, on the other hand, marked hyperemia occurs after 

 three to six hours (more rarely after twelve to twenty-four hours) ; 

 this principally affects the lower lid, the lower portion of the eyeball, 

 the caruncle and the semilunar fold (see Plate VIII). At the same 

 time there is some swelling and secretion, which in severe reactions 

 becomes mucopurulent. 



The height of the reaction is reached after ten to twelve hours, 

 after which the inflammatory manifestations usually disappear and 

 there is a return to the normal. 



While in most cases no unduly severe reactions occur, such have 

 nevertheless been noted in isolated cases, and a number of observers 

 look upon the method in its original form as dangerous and not 

 justifiable. Eppenstein accordingly recommends successive tests 

 with solutions of increasing strength, and the use of both eyes 

 alternately, beginning in adults with a 1 per cent, solution of the 

 old tuberculin, and then increasing to a 2 per cent, and finally 

 to a 4 per cent, solution, while in children a \ per cent, solution 

 is used as the starting dose. 



The existence of any disease of the eye would, of course, constitute 

 a contra-indication to the method in question. 



As regards the clinical value of the Calmette reaction, as com- 



