442 



Mr. W. H. Gaskell on the Action of the [Dec. 14, 



given as thereby to cause a decided tetanus of the muscle, it is possible 

 to observe, under a low power of the microscope, similar phenomena to 

 those that take place in the experiments on the blood-stream in the qua- 

 driceps extensor of dogs that I have already referred to. Upon the com- 

 mencement of the tetanus there is a sudden onward propulsion of the 

 blood in the large veins, followed by a complete stoppage of the blood- 

 stream in them, even sometimes a retrograde stream ; while in the arteries 

 the stream flows steadily on, increasing in rapidity and increasing in 

 fullness ; the arteries dilate, the capillaries on the arterial side become 

 large, filled with blood, very active, and, finally, after a few spasmodic 

 attempts to move onwards, the blood in the veins seems to burst the 

 restraining barriers, moves on more and more rapidly, continually in- 

 creasing in fullness, even though there is still a steady tetanus of the 

 muscle ; and at last, on ending the stimulation, there is seen an extremely 

 rapid, greatly dilated circulation throughout the whole muscle ; gradually 

 and slowly the stream slackens, the arteries contract, and at last there is 

 again a quiet axial stream in the arteries and a slow steady flow in the 

 veins. At the moment of commencing and ending the stimulation there 

 is an instantaneous stop in the arterial flow ; except at these times, the 

 blood flows continuously in the arteries during the whole stimulation. 

 This phenomenon confirms in every particular the observations made by 

 me at Leipzig, and explains most satisfactorily the nature of the curves 

 obtained there. 



By employing larger doses of curare it is possible to examine the effects 

 of nerve stimulation apart from all contraction of the muscle. The fol- 

 lowing facts are observed then, in a thoroughly curarized muscle, upon 

 stimulation of the nerve by means of an interrupted current. Whether 

 the stimulus is long or short, there is always a rapid and very marked 

 dilatation of the artery under examination, which does not commence 

 until some 5 or 6 seconds after the beginning of the stimulation. During 

 this latent period there is not the slightest trace of any constriction, the 

 calibre of the vessel remaining either the same as before the stimulation, 

 or if the stimulation is applied while the artery is dilating or constricting, 

 then this dilatation or constriction continues during this period ; and even 

 if the stimulation is applied at a time w^hen the artery is considerably 

 dilated, there is no trace of constriction, but, on the contrary, a still 

 further dilatation. The maximum of dila.tation occurs about 20 or 30 

 seconds after the commencement of the stimulation, and can be so great 

 that the diameter of the artery may attain to nearly three times that 

 which it possessed originally ; it is always accompanied by a greater 

 rapidity and fullness of the blood-flow, the whole circulation throughout 

 the muscle becoming much more active; it lasts, as a rule, only a few 

 seconds at this maximum height, and then the size of the vessel gradually 

 diminishes to the normal, the blood-stream becoming thinner and rather 

 slower, until, as before the stimulation, there is a steady normal axial 



