18 THE PHYSIOLOGY OF THE ADRENALS. 



and approximation of the vascular walls toward the center of 

 the blood-stream. Where is the need of "reflex inhibition," 

 therefore, to account for slowing of the heart's action, when 

 it is combined with increased power of the heart-muscle? The 

 increase of contractile energy normally implicates a slower 

 action in virtue of familiar mechanical principles. As we have 

 seen, the secretion of the adrenals first appears in the supra- 

 renal veins; it must thence flow into the inferior vena cava 

 and penetrate the heart. It seems apparent to us at least 

 that we need seek no farther for the source of the slowing of 

 the heart, and that it is the result of a direct action of the adrenal 

 secretion upon the cardiac muscle. 



FUNCTIONAL KELATIONSHIP BETWEEN ARTERIES AND 

 THEIR CAPILLARIES UNDER THE INFLUENCE OF ADRENAL 

 SECRETION. The very marked contractile power that supra- 

 renal extract also possesses over the muscular coat of vessels 

 plays an important indirect role in the organism which seems 

 to have been overlooked so far: i.e., that, as capillaries are not 

 supplied with muscles, their walls consisting of endothelial plates, 

 they are not contracted as are arteries and arterioles. 



This embodies two kindred prominent features of pathol- 

 ogy: i.e., the fact that when vessels supplied with a muscular coat 

 contract their capillaries dilate owing to the increased pressure 

 to which the arterial contraction gives rise within the latter, 

 while the opposite relative mechanism when vessels supplied 

 with a muscular coat dilate their capillaries contract prevails 

 owing to the resiliency of the latter when the blood in them 

 recedes. In other words, while, in the first case, the blood is 

 crowded outwardly, in the second it is crowded inwardly. 



The physiological importance of these propositions will be 

 shown in subsequent chapters, but their bearing and soundness 

 seem sustained by the fact that they alone, of all solutions so 

 far advanced, can satisfactorily explain an experimental phe- 

 nomenon a true suprarenal paradox encountered by Lan- 

 glois and Charrin in the course of their earlier laboratory 

 work. 63 These observers, in order to study the action of su- 

 prarenal substance upon toxic agents and toxins, injected equal 



53 Langlois and Charrin: Comptes-Rendus de la Societe de Biologie, July 10, 

 1896. 



