484 Scientific Proceedings (132) 



Although many patient observations have been made on a 

 large number of cats no change in caliber either of the pre- 

 arterioles, the arterioles, capillaries or venules has been seen, 

 nor has the appearance or disappearance of patent capillaries 

 been observed as long as the degree of lung inflation or heart 

 rate remain unchanged. There is therefore no evidence in this 

 research of an active change in the size of the smaller pulmon- 

 ary vessels. 



Effect of Stimulating the Peripheral Vagi Nerves after pre- 

 vious injection of, or painting of Cardiac base with Nicotine. 



Upon stimulation of the peripheral vagi nerves in animals 

 where no change in heart rate occurred, a curious effect is gen- 

 erally observed. With the focus unchanged and a constant lung 

 inflation the vessels appear to pass out of focus, the alveolar 

 air cells appear to bulge, to become more globular and to assume 

 a more glistening appearance. On refocusing, the vessels appear 

 to have sunk deeper into valleys between alveoli. The possibil- 

 ity that these changes may result from stimulation of broncho- 

 motor nerves suggest r self . 



This change in appearance during stimulation of the vagi 

 nerve makes it difficult to be quite certain in regard to changes 

 in the size of individual vessels but observation on 24 different 

 experiments failed to yield any evidence that could be safely 

 interpreted as indicating a change in caliber of any vessel, or 

 an alteration of the blood flow therein. Evidence of vasomotor 

 activity which it was hoped might be revealed by the use of this 

 method could not be adduced. 



Effect of Cardiac Slowing: When stimulation of the peri- 

 pheral vagus nerves in un-nicotinized animals causes a marked 

 cardiac slowing, an unanticipated effect on the blood flow in the 

 visible pre-arterioles and arterioles is noted. During diastole 

 the blood actually flows backward, out of the capillaries and 

 smaller arterioles and toward the larger arteries ; during systole, 

 this is momentarily checked. This reverse flow continues for a 

 few beats only, however, becoming less and less with each heart 

 beat until the flow becomes stationary. Then if slowing is main- 

 tained a gradual onward movement during systole becomes 

 reestablished. This obviously indicates that the pressure in the 

 pulmonary artery and its immediate branches is lower than in 

 the smaller vessels until sufficient time has elapsed to produce a 

 stabilized effect. 



