REGULATING THE CONTRACTIONS OF THE ARTERIES 
35 
detached from the roots of the nerves which sprung from it and removed from 
the canal, immediately after which the artery was found dilated to 13°, but the 
blood had ceased to move in consequence of the feebleness of the heart. 
The experiments upon this animal show that if the brain and anterior 
third of the cord act at all as nervous centres for the arteries of the feet, they 
are certainly not the only parts which possess that function; and also, that 
irritation of any part of the anterior half of the cord gives rise to contraction 
of the arteries of the webs, followed by dilatation, varying much in extent and 
duration, but generally proportioned in both respects to the previous con- 
striction. It is probable that the dilatation would have been greater after the 
last operations, had the heart been working more powerfully ; for it will here- 
after appear that a certain amount of distending force on the part of the blood 
is necessary for the vessels becoming fully expanded. 
And the 18th of April, having put a large frog under the influence of chloro- 
form, I removed a vertebral arch opposite the junction of the middle and pos- 
terior thirds of the scapulae, and then cut across the cord in that situation, 
i.e. rather more than a line anterior to its middle ; a slight retraction of the two 
segments proved that the division had been thoroughly effected. This was 
at 10 o'clock a.m. A few minutes later the arteries had recovered from the 
effects of the irritation ; one selected for special observation, having measured 
12° just before the operation, now varied occasionally between 14° and 1%°, 
and the circulation was rapid through the vessel. The next vertebral arch 
posteriorly having been removed, the cord was divided as far back as it was 
exposed, at roh 23™ 508; immediately after which the web was found ex- 
sanguine in consequence of complete closure of all the arteries, which continued 
almost in the same condition for ten minutes, at the end of which time the 
artery selected was still so small as to transmit single corpuscles with difficulty. 
At ro 35™ the portion of cord included between the points of section was 
detached from the roots of the nerves connected with it and removed from the 
canal. It measured nearly a line in length, and the posterior segment thus 
shortened proved afterwards to be only a very small fraction more than halt 
the length of the cord. The vessels afterwards relaxed slowly, so that at ro! 37™ 
the corpuscles were passing a little more freely through the artery. At rr! 15™ 
the artery measured 14°, but transmitted the blood in a very languid stream ; 
and at noon the evidences of circulation were so equivocal, that I suspected 
the creature, which was weak to begin with, to be dead, though this after- 
wards proved to be a mistake. At ob 45™ p.m. the same state of things con- 
tinued, and the artery still measured 13°, having remained unaltered in calibre 
for the last hour and a half; but I determined to try the effect of irritating 
Dee 
