i66 



THE MECHANISM OF THE CIRCULATION. 



The circulation in the heart is peculiar, because, during each 

 systole, the tension of the ventricular muscle rises above the aortic 

 tension. The blood in the coronary arterioles and arteries is thus 

 driven on into the veins, and back towards the aorta, and the cardiac 

 vessels empty during systole and fill again during diastole. Porter's 

 observations on the veins of the heart, made with minimum manometers, 

 give no support to the view that the heart acts on the coronary circula- 

 tion to any extent as a suction pump, although efficiently as a force 

 pump. 1 A shortening of the diastolic period lessens the nutritive supply 

 to the heart. Similarly, diastolic distension of the left heart by " back 

 pressure" lessens the coronary flow. These are facts of great patho- 

 logical importance. 



Newell Martin 2 observed that the coronary arteries dilated on 

 excitation of the peripheral end of the vagus nerve, and during asphyxia. 

 In the latter case, the dilatation occurred before the rise of aortic 

 pressure. These effects Martin ascribed to the influence of coronary 

 vasomotor nerves. Eoy and Adami 3 also obtained some evidence of 

 the existence of vaso-dilators passing to the heart by the vagus and 

 vaso -constrictors by the sympathetic. 



VASOMOTOR EEFLEXES. 



The arterial pressure is affected reflexly by stimulation of any 

 sensory nerve in the body. Sudden pallor of the face resulting from 

 severe pain, blushing from emotional causes, erection of the cavernous 

 tissue of the genitals from sexual excitement, are examples of common 

 observation. Experimental stimulation of any sensory nerve in the 

 body can produce vaso-constriction ; it may, in certain conditions, 

 produce vaso-dilatation. 



It seems probable that vasomotor reflexes can be excited from 

 excitation of sensory nerves in the walls of the vessels themselves. 4 



In regard to local reflex vasomotor changes, the following observa- 

 tions of Marey are of considerable interest. If the point of a pencil be 

 drawn across the forearm, a white line due to the expression of the 

 blood immediately results. This line rapidly disappears, but after an 

 interval of half a minute reappears once more, and then lasts for some 

 minutes. The white line, on its second appearance, irradiates into 

 neighbouring parts. If the pencil point be drawn down the arm with 

 violence, the primary white line is replaced by a red line. Around this 

 there appears secondarily a white area of some extent. The irradiation 

 of the white area into neighbouring parts, and its slow appearance, 

 suggest that the phenomenon is of reflex origin. 5 



Reflex vasomotor effects generally appear in the vascular area from 

 which the sensory excitation arises. Thus, on stimulating the tongue, 

 the submaxillary gland flushes. 6 On exciting the posterior auricular 

 nerve in the rabbit, the vessels of the ear either first contract and then 



1 Porter, Rep. Brit. Ass. Adv. Sc., London, 1897. 



2 Trans. Med.-Chir. Fac. of Maryland, 1891. 



3 Phil. Trans., London, 1892, vol. clxxxii. B. 



4 Latschenberger and Deahna, Arch. f. d. ges. Physiol., Bonn, 1876, Bd. xii. S. 178 ; 

 Zuntz, ibid., 1878, Bd. xvii. S. 404; Heger, Beitr. z. Physiol. C. Ludwig z. s. Geburtst. 

 yew., Leipzig, 1887, S. 193. 



6 Ann. d. sc. not., Paris, 1858, Zool., Se>. 4, tome ix. p. 68. 



6 Bernard, Journ. dt laphysiol. de Ihomme, Paris, 1858, tome i. p. 656. 



