A COMPARISON OF THE CHARACTERISTICS OF AXONS THROUGH THEIR INDIVIDUAL ELECTRICAL RESPONSES

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Abstract
Individual axons of a nerve (frog) have been identified by their action potentials through the cathode ray oscillograph after amplification up to 2,200,000 times and their properties determined. Threshold shocks elicit responses after a maximum latency of about 0.5[sigma] in fast fibers to over 2.4[sigma] in slow fibers. The latency in a fiber and also the irritability vary, apparently spontaneously, through narrow ranges. The thresholds of induction shocks, condenser charges and constant currents of any given duration increase as the conduction rates decrease, the curves being smooth and hyperbolic in type. The curves expressing the relation of current strength to current duration for individual axons form a continuous series; the slower the fiber the further from the axis is its curve. But plotting chronaxies against conduction rates produces a curve differing wholly from the above; typically the chronaxies of the axons, as their conduction rates diminish, fall uniformly from 0.3 down to 02a (10 m.p.s.) and then rapidly increase. The summation interval of a fiber fluctuates somewhat. In different fibers it shortens as conduction rate slows, down to about 2 m.p.s., and then, possibly due to excessive polarization of the fiber, lengthens rapidly. Excessive polarization, by the testing shock, probably also explains the apparent identity of the absolutely and relatively refractory periods in fibers of low irritability. Otherwise the recovery curves of individual axons form a continuous series; the slower the conduction rate of a fiber the further from the axes is its curve. The amplitude of the action potential appears to decrease linearly as conduction rate, indicating that both may vary as the squares of the fiber diameters. The crest time of the potential increases as conduction rate slows along a curve apparently hyperbolic. Action potentials differing in form and height from the type are not rare; some are accounted for by branching. Excepting chronaxies and summation intervals, the properties of nerve fibers have been found to vary in a perfectly continuous manner through the entire conduction rate range. If there are fiber types the differentiation cannot be made through their objective responses. Consideration is given to the bearing of these results on the interpretation of the significance of the elevations appearing on the conducted action potential of nerves.

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