The Number of Sperms About the Eggs in Mammals and its Significance for Normal Fertilization

Abstract

Figures are given for the numbers of sperms at the site of fertilization in normally mated rats, mice, and sheep, and also in rats and rabbits mated at the time of ovulation or later. For sheep the distribution of sperms throughout the female genital tract is given. In the 4 spp. investigated, the degree of restriction on sperm passage varied between spp. so that the number of sperms at the site of fertilization tended to be inversely related to the size of the site. The concentration at the site would therefore presumably vary relatively little between spp. In normally mated rats higher concentrations of sperms at the site of fertilization were significantly associated with more sperms within the eggs. The usual concentration of sperms at the site is high enough to give all the eggs a good chance of being penetrated before the end of their fertile life, but it is not so high that there is much risk of a disturbance of fertilization through the entry of excess sperms. The frequency of successful sperm-egg collisions was estimated to be 1 every 2 minutes for the rabbit and one every 10 minutes for the rat. The restrictive action of the female genital tract in the rat is evidently relaxed towards the end of estrus, for sperm passage is then facilitated.