On the post-œstrous changes occurring in the generative organs and mammary glands of the non-pregnant dog

The œstrous cycle in animals which come “on heat” at relatively infrequent intervals (i. e. monœstrous animals) has been divided by Heape into the following four periods:— (1) Anœstrum (period of rest). (2) Pro-œstrum (periods of growth and destruction). (3) (Œstrus (period of desire). (4) Metœstrum (period of recuperation, occurring only in the absence of pregnancy). This scheme of classification was adopted by Marshall and Jolly in describing the changes occurring in the generative organs of the Bitch. It has been shown that ovulation normally takes place during œstrus at or near the termination of the sanguineous discharge which characterises the pro-œstrum. This observation has since been confirmed by Keller. Ovulation occurs spontaneously in bitches, the additional stimulus of coitus being unnecessary.