584 CIRCULATION OF BLOOD AND LYMPH. 



dilator fibers and thus allows the effects of the constrictors to mani- 

 fest themselves. Since, however, Bayliss has given evidence to 

 show (p. 568) that the dilator effect in the limbs is due to the anti- 

 dromic action of afferent fibers, it is evident that this important 

 question needs reinvestigation. Various physiologists have shown 

 that muscular activity is accompanied by an increase in the blood- 

 flow through the muscle, as we should expect, but it remains uncer- 

 tain whether this result is brought about solely by an increased 

 activity of the heart or by the combined effect of vasodilatation and 

 increase in heart-work. Kaufmann * takes this latter view in con- 

 sequence of some interesting results obtained upon horses. He 

 measured the blood-flow through the masseter muscle and the 

 elevator of the lip in a horse in which the muscles were exercised 

 normally by the act of eating. The blood-flow was increased as 

 much as five times over that observed during rest, and that this 

 increase was due in part at least to a local dilatation seems to be 

 proved by the fact that the blood-pressure in the artery supplying 

 the muscle fell, while that in the vein rose. While, therefore, our 

 experimental knowledge of the vasomotors of the muscles needs 

 further investigation, we may provisionally accept the view ad- 

 vocated by Gaskell, namely, that the vasomotor supply to the 

 muscles consists essentially of dilator fibers and that these fibers 

 are brought into action reflexly whenever the muscles contract, 

 thus providing an increased blood-flow in proportion to the func- 

 tional activity. It should be added that the local dilatation in 

 the muscles during activity may be due also to the chemical action 

 of the (acid) metabolic products on the blood-vessels (p. 569). 



The Vasomotor Nerves to the Veins. It is assumed in physi- 

 ology that the vasoconstrictors and vasodilators end in the muscula- 

 ture of the small arteries. The veins also have a muscular coat, 

 and it is possible that if this musculature were innervated from 

 the central nervous system we should have another efficient factor 

 in controlling the blood-flow. Mall has given very clear proof that 

 the portal vein receives vasoconstrictor fibers from the splanchnic 

 nerve,f but this supply may be exceptional, as the portal system 

 itself is unique. The portal vein, indeed, plays the role physiolog- 

 ically of an artery in regard to the liver. Roy and Sherrington J 

 give some evidence for the existence of venomotor nerves to the 

 large veins of the neck, and Thompson, as also Bancroft, reports 

 experiments in which it was found that stimulation of the sciatic 

 nerve caused a visible constriction of the superficial veins of the 



* Kaufmann, " Archives de physiologic normale et pathologique," 1892, 

 pp. 279 and 495. 



