DIAGNOSIS OF TUBERCULOSIS 451 



lation is followed by a reddening of the caruncle and usually the 

 conjunctiva as well. The reaction varies in intensity from a very 

 mild local reddening of the caruncle to a conjunctivitis. The reac- 

 tion becomes visible usually in from four to eight hours. The maxi- 

 mum intensity is reached about the twelfth hour and it usually disap- 

 pears within twenty-four to forty-eight hours. If the first test is 

 negative and it is desirable to repeat it with a 2 to 4 per cent, con- 

 centration of tuberculin, the second instillation must be made in the 

 unused eye. The eye first used is sensitized by the first instillation 

 and will react in a severe manner even if the patient has no tuber- 

 culosis. 1 This reaction, however, can only be elicited after ten to 

 fourteen days following the first instillation. 



If tuberculin treatment is to be instituted, the ophthalmo reaction 

 is not indicated, for a reaction is almost certain to take place when 

 tuberculin treatment is established. The ophthalmo reaction should 

 not be used in old people or in individuals having other than perfectly 

 normal eyes. 



5. Specificity of the Tuberculin Reaction. The tuberculin reaction 

 is not absolutely specific as an index of the occurrence within the host 

 of an active tuberculous focus. From 30 to 60 per cent, of adults 

 known -to contain no clinically active foci of tuberculosis, who come 

 to autopsy, show evidences of healed tubercles. In these individuals 

 the tubercle bacillus has been dissolved and its products have sen- 

 sitized them. The tuberculin' reaction, consequently, will be positive 

 in the majority of these individuals because they are sensitized to 

 the proteins of the tubercle bacillus. Young children are much less 

 likely to possess these healed or latent tuberculous foci, and provided 

 they are not too young, or that they are not born of tuberculous 

 mothers, a positive tuberculin reaction is much more conclusive in 

 them. Individuals having advanced tuberculous lesions occasionally 

 do not give a tuberculin reaction. 



Miiller 2 has studied the von Pirquet reaction in young children. 

 His results follow: 



0- 3 months 8.1 per cent, cases with positive reaction 



3- 6 months 7.0 per cent, cases with positive reaction 



612 months 11.7 per cent, cases with positive reaction 



12-24 months 24 . 4 per cent, cases with positive reaction 



In 8 cases with a positive reaction which came to autopsy all were 

 found to be tuberculous; 46 negative cases which came to autopsy 



1 Rosenau and Anderson, Jour. Am. Med. Assn., 1908,.!, 961. 



2 Arch. f. Kinderheilk., 1, 18. 



