The use of the pH-pill has allowed continuous monitoring of vaginal pH during human coitus. In the case of a couple of normal fertility, there was an immediate buffering by seminal plasma so that the vaginal pH changed in 8 sec from pH 4\m=.\3to pH 7\m=.\2.In the case of a couple of low (male) fertility, the immediate effect of the arrival of semen in the vagina was a change from pH 3\m=.\5to pH 5\m=.\5.A similarly small change in pH occurred when the seminal volume of a fertile male subject had been depleted, by repeated ejaculation, to 1 \ m=. \ 5ml. At this pH (5\m=.\5),spermatozoa are generally immobilized.It has been possible to alter normal fertility, as judged by postcoital tests for sperm motility, by the introduction of a pH 3\m=.\6buffer solution into the vagina before coitus. In this latter experiment, the vaginal pH immediately after ejaculation was 5\m=.\0 and, after 2 hr, had reached pH 5\m=.\4.These results in vivo suggest that the vagina is not the hostile environment hitherto imagined, since the normal ejaculate readily overcomes the vaginal acidity by its powerful buffering action. Low seminal volume, with or without a concomitantly low sperm count, and artificial changes in vaginal environment by buffer solutions may affect fertility.

Summary. Intra-vaginal and intra-uterine pressure changes during human coitus were monitored by the use of a pressure-sensitive radiopill.Pressure was found to be negative in the vagina during intromission and male orgasm but became positive during female orgasm. In the uterus, the pressure changes were minimal during male orgasm but increased markedly during female orgasm to a positive pressure of 40 cm H2O2 followed by a sharp fall after orgasm to a negative pressure of 26 cm H2O.The reliability of these results is discussed in relation to their possible significance in the pattern of sperm transport, and it is suggested that the final negative pressure following female orgasm may effect aǹ insuck' of the cervical mucus with its entrapped spermatozoa.

SUMMARY A prolonged study relating plasma testosterone levels to coitus is reported in one male subject. Testosterone levels in samples taken during and immediately after sexual intercourse were significantly higher than those found under resting conditions. A significant difference was not apparent between testosterone measurements taken before and after orgasm, and coitus did not appear to affect plasma luteinizing hormone levels. A marked nyctohemeral rhythm was observed in testosterone levels which tended to be higher early in the day. Masturbation had no significant effect on plasma testosterone levels in seven subjects.

The direct estimation of oxytocin in blood during suckling in women has only been reported by two groups of workers, who obtained conflicting results. Hawker & Robertson (1957) and Hawker, Walmsley, Roberts, Blackshaw & Downes (1961) failed to detect a change in the oxytocin content of peripheral venous blood during suckling. However, Coch, Fielitz, Brovetto, Cabot, Coda & Fraga (1968) demonstrated the presence of oxytocin (12-25 \g=m\u./ml. plasma) in internal jugular venous blood collected from women during suckling. The present study investigates the possible release of oxytocin during suckling and coitus in man by direct estimation of the hormone in the blood. No previous estimation during human coitus has been reported, but in domestic animals an increase in the oxytocin content of the blood has been claimed after mating (Walmsley, 1963) and after artificial stimulation of the genitalia (Fitzpatrick, 1957;Roberts & Share, 1968).Three suckling experiments, with the same multiparous subject (aged 33), were performed at 6, 14 and 18 weeks post partum. In each, a control sample was taken before suckling began, and further serial samples were taken from the start of suckling. Two experiments were carried out during coitus. In the first, a blood sample was taken 1 min. after male and female orgasm, and in the second, samples were taken 5 min. before and 1 min. after male and female orgasm. A control sample was taken several hours before each experiment.The samples (20 ml.) were collected from the antecubital vein into a polyethylene syringe. The extraction and bioassay were those described by Folley & Knaggs (1965). Three recovery experiments were also performed, in which a known amount of oxytocin was added to blood taken from the lactating mother 18 weeks post partum. These samples, together with a blank control, were assayed in the same way.No oxytocin was detected in the first suckling experiment (6 samples). In the second and third experiments (11 samples) oxytocin was found on one occasion each time. Amounts of 112 and 11 /tu./ml. plasma were found in the samples taken 3 min. and 2-5 min. from the commencement of suckling, respectively. In the third experiment, oxytocin was also found in the control sample taken 1 min. before suckling (see Table 1). Oxytocin was found in both cases in the blood sample taken after female orgasm but no activity was found in any of the samples from the male or any of the controls. From the three blood samples with known amounts of oxytocin added, 77, 85, and 96% of the oxytocin was recovered.

This review attempts a critical evaluation of experiments dealing with the process of coitus, and highlights the features which are common to many mammalian copulations. Data for blood pressure changes in the dog and bitch during coitus have been re-analysed and compared with findings for the human. Four criteria for orgasm are suggested, and these are traced through the mammalian kingdom for possible similarities. The question of female climax is discussed and its temporal and qualitative aspects are outlined in relation to the male climax.