444 



THE DYNAMICS OF CARDIAC ACTION. 



But "no flow of blood occurred from the artery, although there 

 was a free escape from an incision in an accompanying vein" in 

 an experiment similar to that previously referred to, also per- 

 formed by Dr. Pratt. In fact, it appears to us very doubtful 

 whether even the capillary communication between coronary 

 arteries and the Thebesian vessels, referred to by the latter 

 observer in his conclusions, at all exists at least in the walls 

 of the right heart. Even disregarding our views, it seems evi- 

 dent that the admixture of venous blood with the arterial blood 

 would greatly reduce and perhaps annul the functional efficacy 

 of the latter as an oxidizing agent. 



We can now understand how the adrenal secretion so 

 greatly influences cardiac activity. An increase of it augments 

 the force of the contraction, but the heart does not dilate as 

 promptly nor perhaps as completely; hence its action is slower, 

 but more forcible; we have seen that this represents the primary 

 effect of all drugs sufficiently active to stimulate the adrenals. 

 A still greater quantity of adrenal secretion increases the vio- 

 lence of cardiac action; the vessels are tense, and ecchymoses, 

 haematuria, epistaxis, etc., may ensue. The heart acts normally, 

 however, in the sense that its diastole is almost complete. Con- 

 tinuous cardiac stimulation through excessive production of 

 adrenal secretion, due in turn to excessive production of iodo- 

 thyrin, as in exophthalmic goiter, causes the heart to contract 

 before it has exhausted its complete diastole and to work 

 within a narrower field. Its contractions are sharp, but rapid: 

 the type of the "cramped heart." Increase of adrenal activity 

 involves increase of oxidizing substance; hence the left heart 

 is correspondingly stimulated. When, however, adrenal insuffi- 

 ciency occurs, the phenomena follow an opposite course; when 

 total inhibition of the adrenal system ensues, the vascular walls, 

 losing all their functional stimuli, the adrenal secretion, the 

 granules /$, and the oxidizing substance, gradually cease their 

 contractions and lapse into diastole. 



THE INNERVATION OF THE HEART. 



We are again brought, by analysis, to the realization that 

 the afferent nerves distributed to the heart incite and govern 

 functional activity but contribute nothing to the continuation 



