440 



Mr. ^Y. H. Gaskell on the Action of the [Dec. 14_, 



apparatus, was enabled to obtain mucliniore satisfactory and trust^Yortlly 

 results than he did. 



Speaking briefly, we found that, in the case of the quadriceps extensor 

 of the dog, stimulation of the anterior crural nerve, by means of the in- 

 terrupted current for a short time, say 15 seconds, caused a considerable 

 outspurt of blood from the muscle-A'ein, followed by a complete cessation 

 of flow, and that at the end of the tetanus there was an immense out- 

 pouring from the vein. 



In the case of a longer tetanus we saw that, following upon the tem- 

 porary cessation of flow, blood again began to stream out, gradually and 

 continuously increasing in volume, until at last, even while the muscle 

 was still in a state of tetanus, there was much more blood flowing from 

 the vein than before the commencement of the stimulation. 



On my return to England, wishing to examine more closely this phe- 

 nomenon, I determined to investigate it, if possible, under the micro- 

 scope in the muscles of the frog ; and rejectiug the tongue, for reasons 

 stated below, I found that the mylohyoid muscle was the most suitable 

 one for my purpose, it being easy to prepare it for microscopic observa- 

 tion without damaging the circulation through it, and, in fact, without 

 even touching the muscle ; whilst, ovdng to its thinness, the small amount 

 of connective tissue in the neighbourhood of the vessels, and the absence 

 of pigment-cells, it is possible here to measure A^-ith a micrometer eye- 

 piece the diameter of vessels more accurately and easily than in any other 

 preparation. 



Upon placing this muscle under the microscope, without having pre- 

 viously touched the nerve, it is seen that the circulation presents much 

 the same character as in the web, the median red-corpuscle stream with 

 an inert layer on each side being plainly visible, although, perhaps ov;ing 

 to the manipulation, the arteries at first are slightly fuller and more 

 dilated than the corresponding vessels in the web. The calibre of the 

 smaller arteries does not, as a rule, remain for any length of time the 

 same, variations taking place somewhat similar to what has often been 

 described in the vessels of the web, but with this difference, that whereas 

 in the so-called " rhythmic contractions of the arteries in the web the 

 artery appears to contract to a certain point and then to return to its 

 original calibre or beyond it, in the arteries of the muscle the vessel 

 appears to dilate from the normal calibre, and then gradually to return 

 to that calibre or below it. These dilatations vary considerably in extent 

 and are absolutely irregular in time, being much less marked both in fre- 

 quency and extent in some frogs than in others, and depend, so it seems 

 to me, probably upon some chance stimulation of the vessels, such as 

 exposure to tke air, &c. 



Upon direct stimulation of the web by means of the interrupted 

 current there occurs a most marked constriction, not only of the arteries 

 between the electrodes, but extending over the whole web, both during 



