VASOMOTOR SUPPLY OF THE ORGANS. 571 



obtained from cats' hearts kept alive by an artificial circulation 

 through the coronary arteries. Stimulation of the vagus slowed 

 the stream (vasoconstrictor fibers), while stimulation of the sympa- 

 thetic path quickened the flow (vasodilator fibers). Neither Maas 

 nor Porter gives conclusive proof that the heart musculature 

 was not affected by the stimulation. Schaefer,* on the con- 

 trary, gets entirely opposite results. When an artificial circulation 

 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 adrenalin into the 

 coronary circulation had no influence upon the outflow, and since 

 this substance causes an extreme constriction in the vessels of organs 

 provided with vasoconstrictor fibers the author concludes that the 

 coronary arteries have no vasomotor nerve fibers. It is evident 

 from a consideration of these results that the existence of vaso- 

 motor fibers to the heart vessels is still a matter open to investi- 

 gation. 



Vasomotors of the Pulmonary Arteries. The pulmonary 

 circulation is complete in itself and, as was stated on p. 481, it 

 differs from the systemic circulation 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 greatef than in the systemic circuit, 

 that is, a larger portion of the energy of the contraction of the 

 right ventricle is used in moving the blood. From the mechanical 

 conditions present it is obvious 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, last, 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 possibility of the effects being 

 due indirectly to the systemic circulation. Bradford and Dean,f 

 by comparing carefully the simultaneous records of the pressures 

 in the aorta and a branch of the pulmonary artery, came to the 

 conclusion that the latter may be affected independently by stimu- 

 lation of the third, fourth, and fifth thoracic spinal nerves, and 

 hence concluded that these nerves contain vasoconstrictor fibers 

 to the pulmonary vessels, the course of the fibers being, in general, 

 that taken by the accelerator fibers to the heart, namely, to the 



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

 t Bradford and Dean, " Journal of Physiology/ ' 16, 34, 1894. 



