CHAPTER XXXIII. 



THE VASOMOTOR SUPPLY OF THE DIFFERENT 

 ORGANS. 



There are three important organs of the body — namely, the 

 heart, the lungs, and the brain — ^in which the existence of a vaso- 

 motor supply is still a matter of uncertainty. A very great deal 

 of investigation has been attempted with reference to these organs, 

 but the technical difficulties in each case are such that no entirely 

 satisfactory conclusion has been reached. A brief review of some 

 of the experimental work on record will suffice to make evident the 

 present condition of our knowledge. 



Vasomotors of the Heart. — ^The coronary vessels lie in or on 

 the musculature of the heart. Any variation in the force of con- 

 traction or tonicity of the heart muscle itself will therefore affect 

 possibly the caliber of the arterioles and the rate of blood-flow in the 

 coronary system. At each contraction of the ventricles the coro- 

 nary circulation is probably interrupted by a compression of the 

 smaller arteries and veins, and the size of these vessels during dias- 

 tole will naturally vary with the extent of relaxation of the cardiac 

 muscle. Since stimulation of either of the efferent nerves supplying 

 the heart, vagus and sympathetic, affects the condition of the mus- 

 culature, it is evident at once how difficult it is to distinguish a 

 simultaneous effect upon the coronary arteries, if any such exists. 

 Newell Martin* found that stimulation of the vagus causes dilata- 

 tion of the small arteries on the surface of the heart as seen through 

 a hand lens. Moreover, when the heart is exposed and artificial 

 respiration is stopped the arteries may be seen to dilate before 

 the asphyxia causes any general rise of arterial pressure. Martin 

 interpreted these observations to mean that the coronary arteries 

 receive vasodilator fibers through the vagus. Porterf measured 

 the outflow through the coronary veins in an isolated cat's heart 

 kept alive by feeding it with blood through the coronary arteries. 

 He found that this outflow is diminished when the vagus nerve 

 is stimulated, and hence concluded that the vagus carries vasocon- 

 strictor fibers to the heart. MaasJ reports similar results also 

 obtained from cats' hearts kept alive by an artificial circulation 

 through the coronary arteries. Stimulation of the vagus slowed 



* Martin, " Transactions Medical and Chirurgical Faculty of Maryland," 

 1891. 



t Porter, " Boston Medical and Surgical Journal, " January 9, 1S96. 

 j Maas, " Archiv f. die gesammte Physiologie, " 74, 281, 1899. 

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