The need for spermatozoa to undergo a physiological change in the female genital tract before they can penetrate ova was described by Austin (1951, 1952) and Chang (1951, 1955).
It has been demonstrated that rabbit spermatozoa survive for as long as 48 hr in the uterus of an oestrous rat. Incubation of rabbit spermatozoa for different lengths of time in the rat uterus resulted in the fertilization of a high proportion of rabbit ova when the spermatozoa were injected into the Fallopian tube 12 to 13 hr after an ovulation-inducing injection of gonadotrophins (Bedford & Shalkovsky, 1967; Hamner & Sojka, 1967). However, if spermatozoa were injected 14 to 14½ hr after the gonadotrophins, practically no ova were fertilized (Bedford & Shalkovsky, 1967). An inference was that only partial capacitation of rabbit spermatozoa had taken place