Of 89 persons tested before the onset of mumps, 89 per cent exhibited erythematous reactions 10 mm. or less in diameter and 95 per cent, reactions 15 mm. or less in diameter.

Of 40 persons tested during the first 5 days of mumps, 95 per cent exhibited reactions 10 mm. or less and 98 per cent reactions 15 mm. or less.

Of 480 exposed persons the attack rate of mumps was 46 per cent among 340 with reactions 10 mm. or less and 10 per cent among 240 with reactions greater than 10 mm. The attack rate was only 2 per cent among 161 with reactions exceeding 15 mm.

The attack rates in 13 skin-tested groups which were exposed to mumps tended to be inversely proportional to the incidence of reactions exceeding 10 mm.

The incidence of reactions exceeding 10 mm. was approximately twice as high among 529 adults (persons 18 years or older) as it was among 306 children (persons under 18 years).

Of 179 adults giving positive histories of mumps, 82 per cent exhibited skin reactions exceeding 10 mm. In certain groups the correlation between history and positive skin test was as high as 0.9. Of 132 adults giving negative histories, 58 per cent exhibited skin reactions of this magnitude. The proportion of reactions exceeding 10 mm. in a small number of children giving positive histories was 75 per cent. The proportion of reactions less than 10 mm. was 15 per cent.

Of 167 adults with positive complement fixation tests, 87 per cent exhibited skin reactions exceeding 10 mm. Of 111 adults with negative complement fixation tests, 52 per cent exhibited reactions exceeding 10 mm. Of 43 children with positive complement fixation tests, the skin test reactions exceeded 10 mm. in 70 per cent. The skin reactions exceeded 10 mm. in 29 per cent of 105 children with negative complement fixation tests.

In 69 of 72 individuals in whom skin reactions exceeded 10 mm., complement-fixing antibody either appeared in the blood or increased in amount within about 2 weeks after the tests were done. Such antibody responses likewise were observed in 34 of 76 individuals in whom skin reactions were 10 mm. or less. The data summarized up to this point were obtained with virus derived from the infected parotid gland of monkeys.

The results of simultaneous tests in 82 individuals employing materials prepared from infected monkey parotid gland and amniotic membrane of chick embryos infected with mumps virus indicated in general that the same individual responded in a similar manner to both antigens. In many instances, however, the membrane material produced weaker reactions. Occasionally an individual failed to react at all to one of these materials but did respond to the other.