REGULATING THE CONTRACTIONS OF THE ARTERIES 39 
J 
was sometimes small, when the other, though in the same web, was large ; 
and not only was there no proportion between the degrees of contraction in the 
two vessels, but in one and the same artery the amount of constriction was 
very different at different parts. The unusual character of these contractions 
implied that they were caused by some unwonted circumstances; and from 
their coincidence with the almost total arrest of the blood, as well as from the 
fact that in the left foot, where the circulation continued free, the arteries 
remained of full size till the animal was destroyed, I was led to conclude that 
the puzzling appearances in question must be in some way or other dependent 
on the cessation of the flow of the vital fluid through the vessels. If this were 
so, it seemed probable that the mechanism by which these irregular contrac- 
tions were induced might be as local as their exciting cause, in which case they 
would be seen to occur in an amputated limb. In order to determine this 
point I made the following experiment. On April 2, 1858, having passed 
a knife between the brain and cord of a large frog so as to render the legs in- 
sensible, and having ascertained that the arterial constriction resulting from 
that operation had subsided, I placed a ligature round one of the thighs, and 
then amputated the limb at a higher point. The application of the ligature 
not only prevented the blood from escaping, but produced considerable tension 
in the soft parts of the thigh ; and on examining the webs, I found the arteries 
fully dilated, one which I selected for special observation measuring 43° in 
diameter. At 6 p.m., an hour and a half after the amputation, the vessel 
still maintained the same calibre, but at 7! 35™ it was slightly less, viz. 4°, 
which was still its measurement at 11 o’clock. Hitherto no change distinctly 
referable to vital contractility had taken place, but on the following morning 
the vessel-was reduced to 3° in diameter, and on the 4th of April it was of 
different sizes in different parts, viz. from 1I$° to 3°, and varied somewhat 
during the course of the day. Still more striking changes in the diameter of 
the artery appeared on subsequent days; thus the vessel was sometimes con- 
stricted to absolute closure in one part of its course, and dilated to a very con- 
siderable degree, e.g. 34°, in another part. More commonly, however, the 
artery, though never uniform in size as in health, had a general tendency either 
to moderate constriction or dilatation. The variations occurred frequently 
during the twenty-four hours, and on one occasion I saw the artery in the act 
of slow contraction at one part driving the blood into a dilated portion at a 
little distance. So late as the evening of the roth of April, i.e. during the ninth 
day after amputation, far later than vital contractility is generally believed 
to last in a limb so circumstanced, variations of calibre continued to show 
themselves; but on the 11th of April the vessel had an almost uniform width 
