Physiology of the heart of a scorpion

Abstract

In view of the fact that scarcely anything is known about the physiology of the hearts of arachnids except that of Limulus, the present investigation on the nature of the heart of Palamnaeus bengalensis C. Koch and the effects of stimuli, pH and drugs on it was undertaken. The hearts were isolated in a saline (pH 6.3) containing sodium chloride, 0.65 gm., potassium chloride, 0.03 gm., and calcium chloride, 0.03 gm. in 100 c.c. of distilled water and the pH maintained with a phosphate buffer. The haemolymph was found to be on the acid side of neutrality, in agreement with Maluf's statement; hence the selection of an acidic saline. Heart-beat after isolation was slow and irregular for nearly ten minutes. On recovery, it showed a high degree of automatic movement with incessant rhythmic and simultaneous beat throughout the myocardium, at a rate of 56-62/min. at room temperature (25-27° C.), without rest pauses. After 10-12 hr. its rate and amplitude fell gradually. After temporarily inhibiting the heartrate by such mechanical stimuli as shaking the saline or pressing the heart, there was acceleration of the rate of beat. Isolated pieces of the heart beat for some time.