VASOMOTOR SUPPLY OF THE ORGANS. 615 



the stream (vasoconstrictor fibers), while stimulation of the 

 sjnnpathetic path quickened the flow (vasodilator fibers). Neither 

 Maas nor Porter gives conclusive proof that the heart musculature 

 was not affected by the stimulation. Wiggers reports* that the 

 effect of epinephrin upon a heart perfused through the coronary 

 arteries, but not beating, is to decrease the flow, while upon the 

 beating heart this effect is reversed, owing to the action of the 

 epinephrin upon the heart contractions. Schaefer,t on the con- 

 trary, gets entirely opposite results. When an artificial circula- 

 tion was maintained through the coronary system and the amount 

 of outflow was determined, he found that this quantity was not 

 definitely influenced by stimulation of either the sympathetic or 

 the vagus branches. Moreover, injection of epinephrin into the 

 coronary circulation had no influence upon the outflow, and since 

 this substance causes an extrem.e constriction in the vessels of 

 organs provided with vasoconstrictor fibers, the author concludes 

 that the coronary arteries have no vasomotor nerve fibers. Lang- 

 endorff reports that strips of coronary artery suspended in an epi- 

 nephrin solution exhibit relaxation instead of the contraction shown 

 by other arteries, and this fact, if corroborated, might be considered 

 as evidence for the presence of vasodilator fibers. It is evident 

 from a consideration of these results that the existence of vasomotor 

 fibers to the heart vessels is still a matter open to investigation. 



Vasomotors of the Pulmonary Arteries. — The pulmonary 

 circulation is complete in itself, and it differs from the systemic cir- 

 culation chiefly in that the peripheral resistance in the capillary 

 area is much smaller. Consequently the arterial pressure in the 

 pulmonary artery is small, while the velocity of the blood-flow is 

 greater than in the systemic circuit, — that is, a larger portion of 

 the energy of the contraction of the right ventricle is used in mov- 

 ing the blood. From the mechanical conditions present, it is ob- 

 vious that the pressure in the pulmonary artery might be increased 

 by a vasoconstriction of the smaller. lung arteries, or, on the other 

 hand, by an increase in the blood-flow to the right ventricle through 

 the venae cavae, or, lastly, by back pressure from the left auricle when 

 the left ventricle is not emptying itself as well as usual on account 

 of high aortic pressure. While it is comparatively easy, therefore, 

 to measure the pressure in the pulmonary artery, it is difficult, in 

 the interpretation of the changes that occur, to exclude the possi- 

 bility of the effects being due indirectly to the systemic circula- 

 tion. Bradford and Dean, J by comparing carefully the simul- 

 taneous records of the pressures in the aorta and a branch of the 

 pulmonary artery, came to the conclusion that the latter may 



* Wiggers, "American Journal of Physiology," 1909. Proceedings of 

 the American Physiological Society. 



t "Archives des sciences biologiques," 11, suppl. volume, 251, 1905. 

 i Bradford and Dean, "Journal of Physiology," 16, 34, 1894. 



