THE HEAT LIBERATED BY THE BEATING HEART

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Abstract
By wrapping the tubular shaped heart of the king-crab around the "warm" junctions of an insert thermopile, the temperature variations during successive beats of the surviving and spontaneously beating organ were recorded. Simultaneously tension or pressure changes were also recorded. Three hearts were so studied. The results were put in terms of calorie production per beat per gm. muscle per gm. tension exerted; in 1 case the tension is calculated from internal pressure changes observed per cm2 of heart wall. One of the hearts yielded results varying as much as 1 : 11. In the other 2, the results were more uniform and from these it appears that the total heat in calories over to the tension exerted is of the same magnitude as was observed by the same author for terrapin ventricle (1922). The initial or anoxi- dative heat was not observed but assuming it to bear the same ratio to the total heat as was observed for terrapin ventricle, the author finds a value for the ratio, Hi/T, that is very nearly the same as was found not only for terrapin ventricle but also for frog''s gastrocnemius muscle (1925). The averages for the 3 organs are 2.8, 2.7, and 2.8 (Xl0-5 calorie) respectively. It is pointed out that since these values are characteristic for muscles answering to single, short lasting rather than to tetanic stimuli, this study of heat production in the Limulus heart yields evidence favoring the view that the intrinsic, normal stimulus to beat in this organ is of momentary single volley type rather than the prolonged tetanic type of stimulation as was proposed by P. Hofmann (1911).

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