CARDIOREGULATION IN LIMULUS. I. PHYSIOLOGY OF INHIBITOR NERVES

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Abstract
1. A method of monitoring heart function in the intact Limulus is described. 2. Isolated hearts had rates ranging from 17 to 28, with a mean of 21.6 beats/min. The rate for any individual heart remained nearly constant (s = 1.89) over a period of hours. 3. Heart rate in intact animals ranged from 15 to 23, with a mean of 18.7 beats/min. The rate for any individual animal remained nearly constant (s = 0.36) over a period of hours. 4. Electrical stimulation of the last two pairs of nerves leaving the hindbrain causes a slowing in heart rate which is dependent on stimulus strength and frequency. Maximum slowing occurs with stimulation frequencies between 10 and 80 cycles/sec. and a lesser slowing at frequencies outside this range. 5. Changes in heart rate are not tightly coupled to stimulation of the inhibitor nerves. A time lag in response occurs both at the beginning and the end of stimulation periods.

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