88 THE INVOL UNTAR Y NER VO US S YSTEM 



was still contracted. It seemed at first possible to attribute this 

 great increase in the flow through the muscle to the mechanical 

 effect on the blood vessels of the muscular contraction, for it was 

 well known that if the rate of flow of blood through an organ is 

 measured, and then for a time the blood is not allowed to flow 

 through, upon the resumption of the circulation the rate of flow 

 is seen to be markedly quicker than at the beginning of the ex- 

 periment ; an artificially produced condition of anaemia is always 

 followed by hyperaemia of the organ. Such an explanation will 

 not account for the great increase of flow when a muscle con- 

 tracts ; for, firstly, the contraction compresses the veins more than 

 the arteries, and, secondly, I have found that a stimulus of the 

 crural nerve lasting only four seconds causes a very much larger 

 increase in the blood flow through the quadriceps extensor 

 muscles than is produced by clamping the artery or vein to or 

 from those muscles for as long as thirty minutes. There is cer- 

 tainly something more than can be explained by mechanical ob- 

 struction to the flow. 



If curare be given in a sufficient dose, then there is no sign of 

 either muscular contraction or increased flow upon stimulation of 

 the crural nerve, although the increase of flow which follows 

 upon section of the nerve due to the removal of vaso-constrictor 

 influences is still manifested. If the curare was only just suffici- 

 ent to prevent any visible contraction of the muscles, I found 

 that stimulation of the nerve, especially by a series of cuts in it 

 (crimping), was followed by a distinctly increased flow of blood 

 through the muscles. This effect of curare pointed distinctly to 

 a close connexion between the contraction of the muscle and 

 the increase of the flow of blood through it, without the inter- 

 vention of vaso-dilator nerves. On the other hand it was known 

 that, although curare did not alter the activity of vaso-con- 

 strictor nerves, there was evidence that it prevented the activity 

 of such nerves as the cardiac vagus, the nervus erigens, etc. 

 On these grounds it seemed to me possible that the vascular 

 dilatation was due to vaso-dilator nerves in the crural nerve, 

 which were paralysed by curare in a sufficient dose. On the 

 other hand, it seemed to me that it was also possible to explain 

 the increase of blood flow by the direct action of the muscular 

 contraction, if the acid products produced by the contraction of 

 the muscles were capable of relaxing the arterial muscular coat. 



