14 THE HARVEIAN ORATIOX, 1894. 



is one of the greatest importance, and one that has hardly 

 received, as yet, the attention which it merits. One consequence 

 of it is obvious — viz., that contraction of the cutaneous vessels, 

 such as occurs upon exposure to cold, will drive more blood 

 through the muscles, and as oxidation goes on more rapidly 

 in them the result will be increased production of heat. 



^ The experiments I have just mentioned show that the vessels 

 of the muscles are not controlled by the vaso-motor centre in 

 the medulla oblongata in the same way as those of the intestine 

 and skin. How far their vascular centres may be associated 

 with those for voluntary movements, which have been so 

 admirably localised by Ferrier in the cerebral cortex, still 

 remains to be made out. The circulation through the muscles 

 is indeed a complex phenomenon, and it was shown by Ludwig 

 and Sadler to depend upon at least two factors having an 

 antagonistic action. When a muscle is thrown into action, it 

 mechanically compresses the blood vessels within it, and thus 

 tends to lessen the circulation through it, but at the same time 

 the stimulus which is sent down through the motor nerve and 

 calls it into action, brings about a dilatation of the vascular 

 walls, and thus increases the circulation through the muscle. 



When the amount of blood is measured before, during and 

 after stimulation of the motor nerve, it is sometimes found 

 that the flow is diminished, at others that it is increased. This 

 difference depends upon the comparative effect of the mechani- 

 cal compression of the vessels of the muscles just mentioned, 

 and upon the increase of their lumen by the dilatation of 

 their walls. It invariably happens, however, that after the 

 muscle has ceased to act, the flow of blood through the muscle 

 is increased. This increase is quite independent of any altera- 

 tion in the general pressure of blood in the arteries, and it 

 occurs when an artificial stream of blood, under constant pres- 

 sure, is sent through the muscle. The dilatation in the muscular 

 vessels, as indicated by the increased flow of blood, and con- 

 sequent change of colour in the frog's tongue, w^as observed by 

 Lepine after stimulation of the peripheral ends of the hypo- 

 glossal and glossopharyngeal nerves,* and the actual changes 



* Lepine, Ludwig's Arheiten, 5ter Jahrg., 1870, p. Ill, 



