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.

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Thirty-five patients fitted with 16 different pacemaker models (from 6 manufacturers) were exposed to 50 Hz electric fields up to a maximum of 20 kV/m. Four different response patterns were encountered: (1) normal sensing and pacing in all Medtronic and some Vitatron units; (2) reversion to the fixed (interference) rate in all Telectronics, all Pacesetter, some Vitatron and CPI units; (3) slow and irregular pacing in one CPI and in all Cordis units; (4) mixed behavior over a critical range of field strengths in which slow and irregular pacing preceded reversion to fixed-rate, in some Telectronics and Pacesetter units. The field strengths required to induce such behavior varied from unit to unit and from model to model, with Telectronics being the most sensitive. In general, the interference threshold depended on the magnitude and distribution of induced body current relative to the pacemaker as well as field strength and thus varied with patient height, build and posture. While only a small proportion of pacemaker patients are likely to encounter electric fields strong enough to interfere with pacemaker behavior, this possible hazard should be recognized.