1876.] 



Vaso-motor Nerves of Striated Muscle. 



441 



the stimulation and for some little time after the stimulation is oyer. 

 If, however, the electrodes are applied directly to this muscle, even to 

 that part which is furthest removed from the point of entrance of the 

 nerve, it is possible, by careful focusing, to see that even during the 

 tetanus of the muscle, provided that that tetanus is slight, instead of a 

 diminished flow, instead of a marked constriction of the arteries through- 

 out the muscle, there is, not only after the stimulation has ceased, but 

 even during the tetanus itself, a most marked increase in the fullness of 

 the vessels, a much greater rapidity of stream, and a very considerable 

 dilatation of the smaller arteries, even to a larger extent than the doubling 

 of the diameter; and if at the same time the circulation through the 

 muscle is very languid, the arteries constricted, and many of the capil- 

 laries empty, a slight stimulation of the muscle itself is all that is neces- 

 sary to cause a rapid full flov/ through the whole muscle. Whether the 

 arteries immediately between the electrodes contract, I cannot yet say ; 

 I can, however, affirm positively that there is no contraction of the 

 smaller arteries situated but a slight distance from the electrodes, or if 

 there is, it must take place in the very short space of time necessary for 

 refocusing on the artery under observation, as in every case, as soon 

 as I have been able to measure the calibre again, I have found it con- 

 siderably dilated. Here, then, is a marked diference between the web and 

 mylohyoid on direct stimulation. 



As to the effect of section of the nerve, I have always noticed that it 

 is followed by a decided reddening of the corresponding muscle, the 

 difference of colour being manifest, as previous to the section the two 

 mylohyoid muscles are always equally pale. Upon closer examination, by 

 first putting the muscle in position under the microscope and then cutting 

 the nerve, it is seen that about 5 to 6 seconds after section the arteries 

 dilate very rapidly, the dilatation soon reaching a maximum, in perhaps 20 

 or 30 seconds, and then gradually diminishing until the original calibre 

 is reached, some 4 or 5 minutes after section — that is, the dilatation caused 

 by section of the nerve is not a lasting one, but is exceedingly similar to 

 that caused by slight mechanical stimulation of the nerve ; for whether its 

 peripheral extremity is pinched by a pair of forceps, or dipped into con- 

 centrated salt solution, or still more markedly when cut and torn by 

 scissors and forceps, there always occurs after a brief latent period of a 

 few seconds, during which there is no trace of constriction, a consider- 

 able rapid dilatation of the artery, which lasts but a short time, and then 

 gradually gives way to a return to the original calibre, and is always 

 accompanied by a more active very fidl stream, the inert layer having 

 wholly disappeared, and the red corpuscles being crowded together to the 

 very edge of the vessel. Here, then, is another marked difference between 

 the web and the muscle. 



If the peripheral end of the nerve is stimulated with a fairly strong 

 interrupted current, so slight a dose of curare having previously been 



