INHIBITORY NERVES TO THE VASCULAR SYSTEM 89 



My observations upon the circulation through the mylohyoid 

 muscle of the curarized frog, in which the muscle was spread 

 out under a microscope and the size of the small arteries directly 

 measured by a micrometer eyepiece, showed the dilatation of the 

 arteries upon stimulation of the mylohyoid nerve even when there 

 was not a trace of contraction of the mylohyoid muscle. This 

 dilatation was not passive, caused by a possible stimulation of 

 sensory nerves, for I observed simultaneously the circulation in 

 the web and in the mylohyoid, and there was no constriction of 

 the blood vessels in the web when the mylohyoid vessels dilated ; 

 again, conversely, if on sensory stimulation the vessels of the web 

 were made to constrict, no marked dilatation of the mylohyoid 

 vessels was caused. These experiments thus pointed in favour 

 of the vaso-dilator nerve hypothesis. 



On the other hand I found that a very dilute solution of 

 lactic acid (i in 15,000 normal saline solution) caused a power- 

 ful dilatation of the blood vessels of the mylohyoid muscle, which 

 was most striking and in marked contrast to the constricting 

 action of a very weak alkaline solution. I concluded from this 

 series of experiments, that it was perfectly possible for a muscle 

 to increase automatically the amount of blood flowing through it 

 when it contracted, because it would alter the chemical constitution 

 of the lymph fluid in it, by the formation of acid metabolites ; and 

 this more acid lymph on its way to the larger lymph vessels bathes 

 and must affect the muscles of the fine blood vessels owing to the 

 looseness of their adventitia. These experiments pointed directly 

 to the activity of the muscle being itself the cause of the vascular 

 dilatation without the intervention of special vaso-dilator nerves. 



About the same time Severini put forward the view that 

 the increased flow of blood through an organ, when it is in a 

 condition of activity, is due to the trophic dilatation of the capil- 

 laries, and not to relaxation of the vascular muscles. He stated 

 that oxygen diminishes the size of the capillary lumen, because 

 the nucleus of the cells of the capillary wall (nucleus of Golubew) 

 becomes more spherical, while conversely with the action of CO 2 

 it flattens out in the cell and so the lumen is greater. Apart 

 from the fact that other observers have been unable to see any 

 such alterations in the shape of the nucleus, my experiments on 

 the vessels of the mylohyoid show clearly that the small arteries 

 do dilate, and therefore any explanation of vascular dilatation 



