488 THE TUBERCLE BACILLUS GROUP 
intensity is reached about the twelfth hour and it usually disappears 
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 concentration of 
tuberculin, the second instillation must be made in the unused eye. 
The eye first used is sensitized l)y the first instillation and will react 
in a severe manner even if the patient has no tuberculosis.^ This 
reaction, how^ever, 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 indicatefl, 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. 
Muller^ 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 
6-12 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 
were all free from tuberculosis, except 1 which had subsequently 
developed miliary tuberculosis. His general conclusion is that the 
unreliability of this reaction increases with age. 
Von Ruck'' has collected a large series of cases from the literature 
with the following results: 
Subcutaneous reaction, 8108 cases in all: 
4803 tuberculous patients (clinical) 4318 positive reaction 
485 suspected cases (clinical) 318 positive reaction 
2820 clinically non-tuberculous 1444 positive reaction 
• Rosenau and Anderson: Jour. Am. Med. Assn., 1908, 50, 961. 
2 Arch. f. Kinderheilk., vol. 50, p. 18. 
5 Beitr. z. Klin. d. Tuberkulose, 1909, 13, 93. 
