REGULATING THE CONTRACTIONS OF THE ARTERIES 29 
the stimulus is transmitted to the arterial coats." Waller and Budge’s experl- 
ments, on the other hand, appear to show that it is from the cord that the 
sympathetic derives its controlling power over the arteries. This discrepancy 
upon a matter of such great importance in physiology appeared to me to 
demand further inquiry,? and I propose in the present paper to communicate 
the result to which this investigation has led. 
The first experiment which I performed with reference to this subject 
(October 27, 1856), namely, division of the sciatic nerve on one side, gave some- 
what puzzling results. Knowing how difficult it is to judge correctly of 
differences of calibre in the vessels by mere inspection, I tied out both feet of 
a frog (under chloroform), so that a slight movement of the stage of the micro- 
scope would bring either into view, and thus, after performance of the operation 
in one limb, the other foot might serve as a standard of comparison. I then 
selected a particular artery of the left foot for measurement with the eyepiece 
micrometer, and, having noted the lmits between which its calibre varied 
during half an hour, isolated the nerve from surrounding parts by dissection, 
without any material change taking place in the diameter of the vessel. I next 
tied a piece of thread tightly round the nerve, with the effect of causing within 
the first few seconds distinct constriction of the artery, which then gradually 
expanded, and within two minutes had a larger measurement than I had 
previously observed. In other words, the effect of the ligature had been con- 
striction speedily followed by dilatation. But on examining the web half an 
hour later, I found the artery had contracted again to about its usual propor- 
tions ; after a few minutes the amount of constriction was very considerably 
greater, and continued so after division of the nerve above the ligature, and 
on looking at the other foot I found the arteries there similarly contracted. 
During the next twenty-four hours I made frequent careful comparisons of 
the conditions of the arteries in the two feet, and found that they presented 
exactly the same variations in calibre ; being sometimes closely constricted, 
at other times fully dilated in both. The constrictions generally commenced 
a very short time before a struggle of the animal, and gradually subsided when 
it had become quiet. It was thus evident that the arteries had experienced no 
1 ‘Observations on the State of the Blood and the Blood-vessels in Inflammation,’ Med. and Chir. 
Trans., vol. Xxxvi. 
* Since this paper was read, my attention has been called by Professor Goodsir to experiments 
recently performed by Pfliger. Operating upon the large edible frog of the continent (Rana esculenta), 
he succeeded in applying the galvanic stimulus to the anterior roots of the sciatic nerve within the 
spinal canal, with the effect of causing complete constriction of the arteries of the webs, Division of the 
same roots, on the other hand, was followed by full dilatation of the vessels (see Henle and Meissner’s 
Bericht, 1857). Clear proof had thus been given, before my investigation of the subject commenced, 
that the spinal system does influence the arteries of the frog’s foot. 
