The persistence of seminal constituents in the human vagina.

The persistence of spermatozoa, seminal acid phosphatase, choline and seminal bloodgroup antigens in the human vagina after sexual intercourse has been studied and the following results obtained. 1. Spermatozoa were usually found up to 3 days after intercourse and were occasionally found up to 6 days afterwards. Smears without spermatozoa were obtained from swabs taken as early as 28 hours, but remained rare until 2 days after intercourse. 2. Seminal acid phosphatase sometimes remained detectable up to 3 days after sexual intercourse. The test was most useful on swabs taken within 1 day and rarely useful after 2 days. 3. Choline was usually only detectable on swabs taken within 1 day of intercourse and even within this time many negative results were obtained. The probability of positive results declined swiftly after 14 hours. 4. Seminal blood-group antigens were only detected at a useful level on swabs taken within 48 hours of intercourse. The chances of obtaining a positive result decreased swiftly with an increasing time interval after intercourse.