186 IV AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



to conclude that the emptying of the intramural vessels by the contraction 



of the heart favors the flow of blood through the heart-walls chiefly by the 

 diminished resistance which the empty patulous vessels offer to the inflow 

 from the aorta when the heart relaxes. 1 



The Vessels of Thebesius and the Coronary Veins. — The vessels of 

 Thebesius probably have a part in the nutrition of the heart. If a glass tube 

 two or three inches long is tied into the ventricle of the extirpated heart of 

 the cat and tilled with warm defibrinated blood, the heart will begin to beat, 

 and, it' the blood is oxygenated from time to time, may continue its contrac- 

 tions tor many hours, although its only supply is through the vessels of The- 

 besius. If a vein on the surface of the ventricle is incised, the blood which 

 enters the ventricle arterial in color will emerge from the cut vein a dark 

 venous hue. showing that it has given up its oxygen and presumably other 

 nutrient substances on its way through the heart-wall. This experiment also 

 demonstrates a connection between the coronary vessels and the vessels of 

 Thebesius ; the same may be shown by corrosion preparations of hearts, the 

 veins of which have been injected with celloidin. 



The extirpated heart may be kept contracting a longer time, when to the 

 supply received through the vessels of Thebesius is added that which may 

 reach the heart from the auricle by baekffow through the coronary veins, the 

 valves of which are incompetent. 



It is evident that these accessory channels of nutrition must be of impor- 

 tance when the main supply through the arteries is diminished, as in arterio- 

 sclerosis. 2 



Blood-supply and Heart-beat. — The relation between the volume of 

 blood passing through the coronary arteries and the rate and force of the 

 ventricular contraction has been studied by Magrath and Kennedy. 3 Varia- 

 tions in the volume of the coronary circulation in the isolated heart of the 

 cat, unless very considerable, are not accompanied by changes in the rate 

 of beat. The force of contraction, on the contrary, appears to be closely 

 dependent on the volume of the coronary circulation (Fig. 40). 



Distention of the ventricle diminishes the volume of blood flowing 

 through the coronary vessels, except when this effect is compensated by the 

 distention stimulating the ventricle to contract more forcibly, and thus to 

 pump more blood through its walls by alternate compression and expansion 

 of the intramural vessels. 4 



Lymphatics of the Heart. — A rich plexus of lymphatic vessels has been 

 demonstrated in the heart. 8 Valuable information concerning the nutrition of 

 the hearl could probably be gained by the systematic study of these vessels. 



1 Porter: American Journal "/ Physiology, 1S9S, i. p. 145; consult also von Vintschgau : 

 Archiv jiir die gesammte I'hysiolor/ie, 1890, lxiv. p. 79. 

 - Pratt: Tbid., p. 86. 

 :; Magrath and Kennedy: Journal of Experimental Medicine, 1897, ii. p. 13. 



4 I. II. Hyde: American Journal of Physiology, 1898, i. p. 215. 



5 Nystroin : Archiv fur Physiologie, 1897, p. 361. 



