REGULATING THE CONTRACTIONS OF THE ARTERIES 27 
tions and dilatations which occurred in this animal, as well as in the last, after 
irritation of the posterior half of the cord, are curious, and may perhaps be 
considered analogous to rapid action of the heart under the influence of stimulus. 
The fact that the arterial contractions so constantly observed to result from 
irritation of the anterior part of the cord, while it retains its connexion through 
the rest of the cord with the roots of the nerves of the hind legs, fail to occur 
after removal of the posterior two-thirds of the cord, has been confirmed by 
subsequent experiments upon other frogs. It appears to imply that if the 
brain and anterior part of the cord discharge the functions of a nervous centre 
for the arteries of the feet, they do not exert that influence through the branches 
which connect them with the sympathetic, but only through the roots of the 
nerves given off from the more posterior parts of the cord. 
On the 2nd of June, a large frog having been put under the influence of 
chloroform, the vertebral arches were removed, from the sacrum to the pos- 
terior edges of the scapulae, and at o 30™ p.m. the cord was divided imme- 
diately behind the latter situation, i.e. a little behind its middle. The left 
foot being examined shortly after, the arteries were seen to be considerably 
constricted ; one of them, which appeared to be a principal trunk, permitting 
single corpuscles to pass with difficulty, and the contraction became extreme 
after irritation of the posterior segment of the cord with a needle. The whole 
of the exposed part of the cord and the cauda equina, including the chief branches 
of nerves for the hind legs, were then removed (at o# 56™), and when the foot 
was again looked at, at 1! rom, the circulation, which had been previously 
entirely arrested by the contraction of the vessels, was going on rapidly through 
dilated arteries, the one before mentioned now measuring 3°. This, however, 
proved not to be the extreme degree of dilatation of which the vessel was 
capable ; for a stream of water at about 120° Fahr., thrown for perhaps a second 
upon the foot, induced, after brief imperfect contraction, an expansion to 
nearly 4°, which again was followed after a few minutes by a return to 3°. 
This experiment was several times repeated. In the right foot, which had 
not been subjected to the hot water, though necessarily equally affected with the 
other by the removal of the portion of cord, the arteries were found of moderate 
size at 3° 45™, having evidently recovered, to a considerable extent at least, 
their contractile power during the 2? hours which had elapsed since the operation. 
One which at this time measured 12°, became dilated on the application of 
hot water to 3°, and afterwards contracted spontaneously to 2°. 
At 4» 15™ an additional portion of the cord was removed, so as to clear the 
spinal canal as far forward as the anterior third of the scapulae. The arteries 
became at once dilated to some extent, notwithstanding that the heart’s action 
