The collagen content of the cervix of the pregnant mouse was found to be least on day 10 of pregnancy and greatest just before parturition (day 19). Similarly, the weight of cervical tissue was least on day 9 and greatest at parturition (day 20). However, the collagen concentration in the tissue was maximal on day 9 (7\m=.\54% of wet weight) and minimal on day 20 (1\m=.\56% of wet weight) because the collagen content decreased more than the weight during the first half of pregnancy and the weight increased more than the collagen during the latter part of pregnancy. Fluctuations in the trend of results were recorded early in the second half of pregnancy and steady changes were only observed in the last few days before parturition. On the first day post partum, conditions had returned to the oestrous state. The results are discussed with regard to the endocrine state of the animal and comparisons are made with changes in the rat cervix during pregnancy.

SUMMARY.— It has been noted that biochemical and morphological changes occurred simultaneously during the embryogenesis of mouse skin. The onset of histological maturation of collagen fibres coincided with a change in the pattern of the in vitro incorporation of both 35SO4 into the sulphated mucopoly‐saccharide and 14C‐proline into the collagen of whole skin. Simultaneously, an increase in thickness and differentiation of the epidermis and changes in the basement membrane were observed. Thus, by applying a variety of techniques it has been demonstrated that a critical period of skin maturation involving dermis and epidermis is reached on the eighteenth day of embryogenesis in the mouse.

The uterine cervix of the mouse consists of dense connective tissue with smooth muscle and has a small and relatively inextensible lumen in the non-pregnant state (Leppi, 1964). However, the cyclic variation of ovarian hormones results in small changes in cervical dilatability (Crelin, 1958). The present study was undertaken as, unlike the rat, there is a lack of information on the actual collagen content of the mouse cervix throughout the oestrous cycle. It was also felt to be a useful basis for an investigation currently in progress into cervical collagen changes during pregnancy in this species.Albino, virgin mice aged 3-6 months from a closed but not inbred colony were used. Animals with a regular cycle were selected after taking vaginal smears for at least two cycles. Allen's (1922) definitions were used to designate smears as prooestrus, oestrus, metoestrus and dioestrus. On the day of experiment smears were taken from the selected animals just before death, which was caused by chloroform inhalation. After removal of the reproductive tract, the cervical region was dissected away at the bifurcation of the uterine horns and the vagina trimmed off to expose the caudal projection of the cervix. The tissue was weighed immediately and again after overnight drying at 65°C. Collagen was estimated by hydroxyproline assay according to the method of Prockop & Udenfriend (1960).The means and standard errors of wet and dry weights, total collagen, collagen concentration ana percentage water content of cervical tissue at different stages of the oestrous cycle are shown in Table 1. The total collagen and the weight (wet and dry) of the cervix were greatest at oestrus and least at dioestrus. In contrast the collagen concentration (compared with wet or dry weight) was lowest during prooestrus and oestrus and highest at dioestrus. The water content varied only slightly but was marginally higher in the oestrogen-dominated part of the cycle than in metoestrus or dioestrus.Disregarding the slight variation in water content, it appears that the increase in cervical weight at oestrus is due, in only a small proportion, to increased collagen content, and in a much greater proportion to other tissue components, and this results in the overall fall in collagen concentration. This growth differential under the influence of oestrogen has previously been demonstrated in intact rats

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