Abstract
The determination of the electrical characteristics of living systems has been severely limited by the nature of the measuring devices available. During the past year and a half, one of us (H.S. Burr), with the help of C. T. Lane of the Physics Laboratory, has developed a vacuum tube potentiometer which is stable, draws almost no current from the living system and is independent of inter-electrode resistance up to one megohm. With this instrument, it is possible to record accurately minute voltage changes in living systems under a wide variety of circumstances. Furthermore, with the aid of L. F. Nims of the Department of Physiology, reproducible silver-silver chloride electrodes have been made, by means of which many artefacts have been eliminated.
Students of reproduction have long been searching for some external sign of ovulation in order to accurately place this event in the time sequences of the oestrous and menstrual cycles, and for use in dating and controlling conception. Ovulation was not actually observed until 1928. Walton and Hammond 1 first described this process in the rabbit. This animal was chosen for it has long been known that the rabbit ovulates about 10 hours after mating. To extend and reexamine the observations of Walton and Hammond, a moving picture of ovulation in the rabbit has just been completed. 2 This film showed the process of ovulation to be truly explosive in nature and led us to believe that such a rupture should be accompanied by electrical changes of sufficient magnitude to be measurable with the above potentiometer.
Putting this to test, it has been possible to read differences in electrical potential in the following way. Rabbits were mated and approximately 6 hours later were surgically anesthetized with sodium amytal.
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