Simultaneous multiple tuberculin testing.

In experimental work with tuberculin testing-for example, for comparing different testing procedures, for standardizing tuberculin, etc.-two tests are often given to each person. Because of variations in allergy from person to person, such duplicate testing gives a much more precise comparison of two test procedures for a given number of persons than does the alternate use from person to person of two test procedures to be compared. In adopting this method of testing it is tacitly assumed that the two tests in the same person do not interact in any way. The present paper shows, however, that this assumption is not justifiable.The authors describe an experiment in which 611 infants who had been BCG-vaccinated at 2-5 days of age were tuberculin-tested 3-5 months later, 306 of them with a single 10 TU test and 305 with a 10 TU test in one arm and a 100 TU test in the other arm. The results showed that there was a highly significant difference between the two groups, both in the average size of the reactions and in the degree of induration, the single-test group giving the larger and stronger 10 TU reactions.