42 ON THE PARTS OF THE NERVOUS SYSTEM 
some particular region of it. The experiments hitherto related had revealed 
nothing absolutely irreconcilable with the hypothesis of a spot about the middle 
of the cord being the special regulator of the contractions of the vessels; a view 
indicated, though by no means proved, as regards the arteries of the face and 
fore-limbs in mammalia, by the observations of Waller and Budge and of Schiff, 
alluded to at the commencement of this paper. It appeared probable that this 
point might be readily determined by removing the middle third of the cord, 
and ascertaining whether or not the arteries still retained their contractility. 
Accordingly, on August 26, 1857, having selected for measurement an artery 
in one of the webs of a frog, I divided the cord transversely at the distance 
of a quarter of its length from the posterior end, at 114 7™ a.m. During the 
next half-hour the diameter of the vessel was observed varying frequently 
from $° to 14°. At 11! 34™ the cord was again cut across opposite the middle 
of the scapulae, i.e. at a distance of a little more than a quarter of its length 
from the occiput. After this operation the artery was observed for about 
a quarter of an hour varying occasionally in calibre between 1° and 2°. At 
11» 53™ the portion of cord intervening between the two transverse incisions, 
and measuring very nearly half its entire length, was removed, immediately 
after which the artery measured 13°. At 112 55™ its diameter was 1°, the heart 
meanwhile continuing in good action, and twelve minutes later the vessel was 
again seen to change in calibre from 1° to 13° and back again to 1°. The heart’s 
action afterwards became very feeble, and the parts of the nervous centres 
concerned in regulating the arterial calibre appeared also to be failing in their 
functions, the vessel varying very slightly, and gradually increasing in diameter, 
till towards 1! p.m. its measurements were from 2° to 23°. At rh 1™ the 
posterior end of the cord was removed, immediately after which the diameter 
of the artery was above 23°, or larger than ever seen before ; at 1) 4™ it was 
near 24°, and continued so at 1" rom. Soon after this the circulation ceased 
entirely. 
In this case, notwithstanding the removal of the two middle quarters of 
the cord, the arteries were observed moderate in size and varying in calibre 
at a time when the heart was acting well. Hence it was evident that the middle 
portions of the cord are not essential to the regulation of the arterial contrac- 
tions in the feet. The following experiment confirmed this important con- 
clusion, and also furnished additional information. 
On the 20th of October, a large frog having been placed under chloroform, 
* In the original manuscript I was obliged to express my regret that time had not yet permitted 
me to carry out this idea. The dates in the text indicate that it has been done since the paper 
was read. 
