By the 8th day post partum, the human uterus has lost approximately 72 per cent of the total collagen which was present at term. The slopes of curves depicting alterations in collagen content of the uterus of the rat and human are virtually identical, despite the marked differences in the length of the gestational periods of the two species.

The alterations in the collagen content of the human uterus during pregnancy and involution closely follow changes in total uterine weight. There is a slight decrease in per cent collagen content of the uterus during pregnancy, and an increase in the water content of the post partum uterus.

Approximately 97 per cent of the collagen which is present in the human uterus at term is of the so called "insoluble" type. The physiological resorbability of uterine collagen, as evidenced by its post partum dissolution, cannot therefore be correlated with its in vitro solubility characteristics.

No collagenase was demonstrable in the myometrium of post partum uteri. A 2 day post partum uterus was found to contain an enzyme which slowly degraded gelatin at pH 3.85 but was virtually inactive at pH 7,0.

There is an increase in myometrial prolidase activity of approximately 75 per cent, commencing 2 days post partum. Prolidase activity remains elevated until the 8th day post partum, and subsequently falls to almost normal levels by the 5th post partum week.

During the process of involution, the post partum uterus shows histological evidence of edema and partial destruction of its reticular framework.