280 THE HUMAN BODY. 



dance of energy enabling them to work under unfavorable 

 conditions, are less apt to suffer in such ways than their eld- 

 ers. One sees boys running actively about after eating, when 

 older people feel a desire to sit quiet and ruminate or even 

 to go to sleep. 



When the nerve of a limb is cut and its peripheral end is 

 stimulated the usual result is arterial constriction, because 

 the constrictor fibres are more numerous and more powerful 

 than the dilator; a day or two after section, when the nerve 

 has begun to degenerate, stimulation, however, causes dilata- 

 tion, apparently because the constrictor fibres degenerate 

 more quickly: and when the stimuli (as induction shocks) 

 given to the nerve are repeated at only a slow rate the dilator 

 effect frequently overcomes the constrictor. 



The Vaso-dilator Centre. The vaso-dilator nerves, like 

 the vaso-constrictor, seem to originate primarily in a centre 

 in the rnedullaoblongata. In regard to the arteries in general, 

 they play a much less conspicuous part than their analogues, 

 the cardio-inhibitory fibres, do in regard to the heart. 



The Vaso-motor Nerves of the Veins. Most veins have 

 a muscular coat, though it is much less developed than in 

 the arteries, and this coat is probably under the control of 

 nerve-fibres. Satisfactory evidence of their existence is still 

 wanting. 



The Vascular Phenomena of Inflammation. When 

 some transparent portion of an animal (for example the 

 mesentery of a mouse or guinea-pig) is carefully exposed arid 

 studied with a microscope, the normal flow in the small ves- 

 sels may be studied for some time, much as in the web of the 

 frog. If an irritant be applied, the immediate result is a 

 widening of the small arteries and a greater and more rapid 

 flow through them and the capillaries and veins. This seems 

 dependent mainly on a direct paralysis of the arteries, and if 

 the irritant be transient in its influence the congested con- 

 dition soon passes off. If the irritant be more powerful, the 

 vascular dilatation continues and other circulatory changes 

 are seen. The corpuscles, instead of keeping, as is usual in 

 arteries of microscope size, to the central part of the tube 

 (axial current), spread more evenly, and the white cor- 

 puscles especially tend to pass into the layer of liquid in im- 

 mediate contact with the inner coat of the artery, and at the 

 same time to exhibit much more marked amoeboid move- 



