The genesis of inhibition of the cardiac ganglion of limulus by stimuli of increasing frequency

Abstract

The nature of inhibition, whether peripheral or central, remains obscure despite the many sided experimental approaches to the problems by investigators too numerous to mention, vide Howell ('25). The concepts of central inhibition are the result of studies conducted chiefly on vertebrate reflexes where physiological complexity makes analysis difficult if not impossible. Simpler relationships, both anatomi-. cal and physiological, make the ganglionic cord of the heart of Limulus attractive for investigation in this connection. It has been shown that typical inhibition of the autogenous rhythm of the ganglionic impulses results upon faradic stimulation of certain nerve fibers afferent t o the ganglion, and also that direct faradization of the ganglion causes inhibition (Carlson, '04, '05). This latter fact was the initial point of interest which led to the present report. We are familiar with the fact that a single stimulus, either electrical or mechanical, results in a ganglionic discharge and an extra-systole of the of the heart (Garrey, '30; Xamojloff, '30) and the problem before us is to determine how repetition of stimuli, as in faradization, passes from stimulation over into inhibitionwhether we are dealing with two separate and distinct processes or with two phases of a single process.