THE CIRCULATION THROUGH SPECIAL ORGANS 429 



of the musculature. It need not surprise us, therefore, to find that the 

 mechanical influences thus exerted upon the blood stream play an 

 important part in the flow through this system of vessels. In fact, 

 much uncertainty has always prevailed regarding the manner and the 

 time during which the coronary blood-vessels are filled. Brucke,^ for 

 example, has expressed the idea that the heart possesses a self -regula- 

 tory mechanism whereby the circulation through this organ is made to 

 differ in certain particulars from that through other parts of the body. 

 As the orifices of the coronary arteries are situated behind the flaps of 

 the aortic valve, the claim has been made that these openings are com- 

 pletely closed during each ventricular systole^ and that the heart ob- 

 tains its sapply of blood only during the diastolic period when these 

 valve flaps are in the position of closure. This mode of filling seemed 

 the more likely, because the relaxation of the cardiac muscle must exert 

 a favorable influence upon the influx of the aortic blood, while its 

 contraction must force the blood onward into the veins and right 

 auricle. 



This view, however, has found no substantiation, because it has 

 been proved by Martin and S»edgwick,^ as well as by Porter,^ that the 

 pressure changes in the coronary arteries coincide very closely with 

 those occurring in the systemic circuit. Moreover, RebataP has 

 shown that the coronary blood flow suffers an acceleration at the 

 beginning of each systole, but ceases as soon as the musculature has 

 attained a state of maximal contraction. A second augmentation 

 in the flow is said to result during diastole which, however, soon suffers 

 a retardation in consequence of the gradual filling of the right auricle. 

 These data prove, on the one hand, that the coronary circuit remains 

 in free communication with the aorta even during the systole of the 

 heart and, on the other, that the contracting musculature exerts 

 a powerful pressure upon the intramural blood-vessels which greatly 

 favors their emptying. In further substantiation of this statement 

 it might be mentioned that if a piece of ventricle is made to beat 

 rhythmically by perfusing it with a nutritive fluid through its artery, 

 a jet of blood is forced from the distal venous orifice with every 

 contraction (Porter). 



The question whether the coronary circuit is equipped with a 

 vasomotor mechanism has not been decided as yet, because any 

 attempt to solve this problem, either by measuring the blood flow 

 directly or by determining the changes in pressure, must be seriously 

 hampered by the mechanical action of the contracting musculature. 

 Neither is it possible to obtain more accurate data by stimulation of 

 the efferent nerves of the heart, because the vagal and sympathetic 



1 Der "Verschluss der Kranzschlagadern durch die Aorten Klappen, Wien, 

 1855. 



2 A statement generally attributed to Thebesius (1708). 



3 Jour, of Physiol., iii, 1880, 165. 



* Am. Jour, of Physiol., i, 1898, 71. 

 ^ Dissertation, Paris, 1872. 



