1876.] 



Vaso-motor Nerves of Striated Muscle, 



443 



flow. It is not possible to keep up the dilatation for any length of time, 

 so that if the stimulation is long, say a minute or more, before the end of 

 it the vessel may have regained its normal calibre ; and if the stimulus 

 is long enough and strong enough, then it is possible for a secondary effect 

 to be produced in the form of a decided constriction of the vessel follow- 

 ing upon the dilatation and occurring after the stimulation is ended, this, 

 again, being followed by a recovery to the normal diameter. It is thus 

 seen that, while in the case of the web stimulation of the sciatic always 

 causes constriction, followed after strong stimulation by dilatation, in the 

 case of the muscle stimulation of its nerve always causes a dilatation of 

 the vessels, followed, after strong stimulation, by a decided constriction 

 of the same ; so that it seems highly probable that, when the sciatic in 

 the frog is stimulated, constriction in the web is accompanied by dilata- 

 tion in the muscles of the leg, and dilatation in the web .by constriction 

 in those muscles. Moreover, as it is possible to keep up the constriction 

 in the web for a much longer time, by commencing with a weak stimulus 

 and gradually increasing its strength, so I think, too, that the dilatation 

 in the muscle can be made more enduring by the same method. 



Bhythmic stimulation of the nerve, by means of single induction-shocks, 

 repeated at intervals of 2 or 5 seconds, produces the same kind of dilatation 

 as the interrupted current. 



If, as sometimes occurs, owing perhaps to the muscle being over- 

 stretched or some other cause, the circulation through it is found 

 to be nearly stagnant, the arteries constricted, the capillaries barely 

 visible, it is only necessary to stimulate the nerve in order to produce a 

 full active circulation throughout ; and this occurs even daring the stimu- 

 lation; while, under the same circumstances, in the web there is still 

 further stagnation produced, still greater constriction, and it is only after 

 the stimulation has ceased that an increased and more active flow takes 

 place. 



A marked dilatation of the vessel is often seen to occiu* in an appa- 

 rently empty artery before the first rush of blood-corpuscles makes its 

 appearance; and this dilatation does not always occur over the whole 

 vessel at once, but rather parts of the previously constricted vessel appear 

 to bulge out, the intermediate parts remaining still constricted ; so that 

 the vessel has somewhat the appearance of a string of pearls, and gradu- 

 ally as the vessel dilates more and more, and the blood-stream increases 

 in volume and rapidity, the walls of the vessel lose this uneven appear- 

 ance and become uniformly dilated. 



Seeing, then, that even when the blood-current in the muscle is feeble 

 (that is, when the pressure in the vessel is diminished) stimulation of the 

 nerve always causes a marked dilatation, I determined to observe the 

 effect of stimulation when the arterial pressure had been removed by 

 compressiiDg the aorta. 



Directly after the aorta is compressed by a clip a steady, rather rapid con- 



VOL. XXY. 2 I 



