360 EBEN J. CAREY 



the cardiac musculature by a dynamic tensional interaction. The 

 cardiac musculature responds to the optimum stretching stimulus 

 by contraction, thus the circulation is maintained — the blood is 

 driven on. There is a definite mechanical interaction between the 

 circulating blood and the responding heart in contraction. 



AMiatever chemicals are withdrawn from the circulation that are 

 needed to maintain the normal cardiac irritability are bound to 

 affect the beat. All the chemical work that has been accomplished 

 on the heart beat does not vitiate or exclude the extrinsic mechani- 

 cal, tensional stimulus applied by the circulating blood. As 

 regards the extrinsic tensional stimulus of the heart beat, it is 

 haemogenic in nature and, as we have seen definitely, for the striated 

 muscular bladder rhythm it is hydrogenic in nature. We saw in 

 the bladder that the beats were inhibited completely by withdrawing 

 the stimulus. The bladder musculature is not w^ound up in a 

 manner like the heart, in which the muscle layers are related syner- 

 gistically for reciprocal interaction; therefore, it does not present 

 automatic attributes. 



The nervous mechanism regulates and helps to maintain cardiac 

 irritability. The nodal tissues of the heart belong to the reacting 

 body. Any structure intrinsic in the heart contributes merely to the 

 second act in Newton's third law of motion, i.e., the reaction. The 

 primary activator, initiator, or stimulus is the extrinsic, mechanical, 

 hydrodynamic pressure tension produced by the circulating blood 

 which causes tension of the heart muscle just as the water pressure 

 is the stimulus for the rhythmic action in the hydrant force-pump. 



CONCLUSIONS 



1 . The differential degree of energy possessed hy the types of 77iiLScle 

 is purely an emhryological hiomechanical problem corresponding to 

 the diverse amounts of optimum tensile work that has been experided in 

 their formation by a dominant extrinsic energetic zone which draws out 

 the premuscle mesenchyme in traction between the points of attachment 

 at least one of which is mobile. 



2. The elongation of the muscular fasciculi is in the direction of a 

 dominant force extrinsic to the zone of myogenesis, just as the 

 strands of a mass of taffy candy are in the direction of the diverging 

 supports — the hands. 



