The Male Frog, Rana pipiens, as a New Test Animal for Early Pregnancy

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Abstract
The [male] frog, Rana pipiens, has a high diagnostic value as a test animal for early pregnancy. The animals are not killed for the test and may be used again. Urine from women in the last trimester of pregnancy gave nearly 50% false negative results, whereas specimens from the first trimester have given entirely positive results. There have been no false negatives. There were used well over 200 animals with the urines of pregnant women, nonpregnant women, and men. Check animals were untreated frogs and frogs injected with Ringer''s soln. (cold). No check animal has ever produced sperm. The question of seasonal variation is still unknown. A first morning (overnight) specimen of urine is obtained and 5 ml. are injected subcut. into the dorsal or lateral lymph sacs. Two or more frogs are employed. Each frog is placed in a separate, clean, dry glass jar with a perforated lid and held for 2-4 hrs. at room temp. Any urine that has been voided by the frogs is examined microscopically. If sperm are not present, the urine is carefully drained without disturbing the animal. The frog is seized in the hand while still in the jar. The pressure produces another urination; the new specimen is examined for sperm. The test is positive if sperm are present and negative if not. There are no inter-grades. The animals can be used again after 4 or 5 days.

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