Use of vaginal concretions of calcium carbonate to detect ovulation in hamsters

Concretions of calcium carbonate normally appear every third and fourth da of the 4-da hamster cycle da 1 = day of ovulation). We presently found that the 2-da relation between ovulation and concretion formation was maintained even after ovulation was delayed 1 or more da by centrally acting drugs or by exposing the hamsters to constant light. It is therefore possible to identify days of ovulation in vaginal washing records of both normal and treated hamsters by counting back 2 da from each sequence of concretions.