734 



SPERM, OVA, AND PREGNANCY 



1. The Cervix 



This portal connecting the vagina and 

 the uterus is generally regarded as constitut- 

 ing a partial block to sperm transport in cer- 

 tain animals in which ejaculation occurs in 

 the vaginal vault, e.g., the rabbit, ewe, and 

 man (Warbritton, McKenzie, Berliner and 

 Andrews, 1937; Chang, 1951b; Braden, 1953; 

 Noyes, Adams and Walton, 1958). Sperm 

 migration through the rabbit cervix is a 

 gradual process (Florey and Walton, 1932; 

 Braden, 1953) and, although the mechanism 

 certainly is not definitely known, is possibly 

 to be attributed to active flagellation of the 

 sperm themselves, with little or no help from 

 the cervical duct (Noyes, Adams and Wal- 

 ton, 1958; cf. Hartman, 1957). Dead cells, 

 according to Noyes and colleagues, fail to 

 negotiate the cervical passage, as do radi- 

 opacjue media. It should be noted that the 

 latter finding is inexplicably at variance with 

 a similar experiment of Krehbiel and Car- 

 stens (1939), who found that radiopaque 

 medium does pass the rabbit cervix in sig- 

 nificant amounts. Noyes, Adams and Wal- 

 ton (1959) also indicated that estrogen 

 treatment facilitates cervical transport of 

 spermatozoa, that is, decreases the resistance 

 to migration shown by untreated animals, in 

 this case castrated does. Whether the effect 

 is actually on the cervical musculature, the 

 secretion of cervical mucus, uterine motility, 

 or some other system is not clear from these 

 experiments. 



The cervix should not be regarded as al- 

 ways constituting an obstacle to sperm trans- 

 port. In at least two species with intravagi- 

 nal insemination, namely, the heifer and dog, 

 sperm transport is extremely rapid. The 

 cervices in these animals, therefore, rather 

 than retarding progress, must aid consider- 

 ably in the migration of spermatozoa. 



A frequently suggested theory to account 

 for the passage of spermatozoa into the 

 uterus envisages "insuck" of the semen 

 through the cervix. Indeed, a transient nega- 

 tive uterine pressure of about 0.7 lb. per 

 square inch has been demonstrated during 

 coitus in the mare (Millar, 1952). However, 

 the significance of such determinations in 

 this animal is obscure since ejaculation nor- 

 mally occurs directly into the uterus (Braden 

 and Austin, 1953) . Nevertheless, in consider- 



ation of the concept relevant to women, it 

 is reasonable to assume that the uterus can 

 aspirate sperm and mucus into the uterine 

 cavity by virtue of the elasticity of that 

 organ following contraction (Belonoschkin, 

 1949, 1957) . This subject is more extensively 

 reviewed by Hartman (1957). 



Much attention has been focused on the 

 questions of the nature of cervical mucus, its 

 cyclic changes, and its penetrability by sper- 

 matozoa in vitro (Shettles, 1949). The im- 

 portance of cervical mucus is obvious if 

 sperm reside in the cervix for considerable 

 periods of time, as in women, or if the sperm 

 have to negotiate the canal by their own 

 motile faculties; it is of much less signifi- 

 cance when the sperm are shot through the 

 cervical canal at ejaculation, as in the sow, 

 or are carried through rapidly by muscular 

 contractions, as in the heifer. 



The secretory activity of the cervix re- 

 sponds to variations in the ovarian cycle, 

 and the physicochemical composition of the 

 mucus changes accordingly. The response of 

 the cervix to cyclic changes was first clearly 

 stated by Allen (1922) for the mouse. Much 

 of our current understanding stems from the 

 important monograph of Sjovall (1938) 

 concerning investigations of human and 

 guinea pig cervices. There now exists ade- 

 quate evidence that changes in human cer- 

 vical mucus correlate well with ovulatory 

 and with endometrial, vaginal, and other 

 indications of estrogenic activity (Sjovall, 

 1938; Vicrgiver and Pommerenke, 1946; 

 Shettles, 1949; Bergman, 1950; Cohen, Stein, 

 and Kaye, 1952; Odeblad, 1959). Cervical 

 mucus in women is most copiously secreted 

 during the estrogenic phase; its dry weight 

 at this time is minimal (Bergman, 1950), 

 tonicity is low (Bergman and Lund, 1950 », 

 and pH, as generally determined, is elevated. 

 Estrogenic mucus is also claimed to be richer 

 in glucose and polysaccharide, but these 

 components may be derived less from the 

 cervical secretion than from the uterine 

 glands higher in the tract (Bergman and 

 Werner, 1950). Lipid is present in lower 

 amounts at ovulation. Benas (1958) found 

 changes, as determined by paper electro- 

 phoresis, in the extractable protein, with a 

 predominance of albumin in pre-ovulatory 

 mucus and a prevalence of /?- and y-globulins 



