PROGRESS OF MICROSCOPICAL SCIENCE. 299 
piece the diameter of vessels more accurately and easily than in any 
other preparation. Upon placing this muscle under the microscope, 
without having previously touched the nerve, it is seen that the cir- 
culation 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 owing 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 nof, as a rule, 
remain for any length of time the same, variations taking place some- 
what 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 abso- 
lutely irregular in time, being much less marked both in frequency 
and extent in some frogs than in others, and depend, so it seems 
to him, probably upon some chance stimulation of the vessels, such as 
exposure to the air, &e. 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 the stimulation and for some little time after 
the stimulation is over. He goes on to say, ‘“ 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 
refocussing 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 difference 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 
five to six seconds after section the arteries dilate very rapidly, the dila- 
tation soon reaching a maximum, in perhaps twenty or thirty seconds, 
and then gradually diminishing until the original calibre is reached, 
some four or five 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 
concentrated 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 con- 
siderable 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 full stream, the inert 
VOL. XVII. Z 
