Heat Production in Nerve and Electric Organ

Our knowledge of the physical events associated with the passage of an action potential along a nerve probably represents the most precise and detailed information available for any biological process. Yet there is an almost complete absence of knowledge of the specific biochemical changes involved or of the energeties of the action currents. Measurement of thermal changes during such activity can furnish information which may provide clues as to the sorts of chemical processes which may be occurring; while studies on the electric organs of fishes in which the electrical work available can be extracted into an external system, permit thermal and electrical energy changes to be measured under widely differing conditions of loading and so give information on the dynamics of the energy source. The resting heat of nerve, and the heat of the recovery processes, have been studied in detail with an accuracy and precision which cannot at present be improved upon (Feng, 1936). Valuable information could certainly be obtained from further work on these events particularly from comparisons under aerobic and anaerobic conditions. A small burst of heat occurs before the recovery begins, amounting to only 1 or 2 per cent of the recovery heat. The experiments of Beresina and Feng (1933) showed this early outburst of heat in crab nerve at 16.5°C. to be 0.7 X 10 -6 cal. /gm. /impulse, and Feng (1936) estimated that the corresponding value for frog's medullated nerve at the same temperature would be 0.067 X 10 -6 cal./gin. But the slow response of the apparatus made it uncertain whether this heat was really an "initial" heat or only a first part of the recovery process. The experiments I wish to review are those which have been carried out in recent years, using more rapid recording techniques. Thermopiles are still the most suitable detectors of temperature changes for most of the experiments described, although thermistors were used in some instances. The use of rapid stable galvanometers with photoelectric amplification of galvanometer movement, and cathode rayosciUographic recording, provides considerable improvement in time resolution. I t must be remembered that, in general, improvement in time resolution and (temperature) sensitivity move in opposite directions, so that our sensitivity is no greater than it was in the older work referred to; but the time resolution then was poor. With the present equipment the time resolution has been improved so that we can resolve the heat