34 ON THE PARTS OF THE NERVOUS SYSTEM 
induced by the irritation of the anterior part of the cord in the operation, 
followed by a brief period of dilatation. At 4", a small part of the spinal canal 
having been laid open, the anterior sixth of the cord was removed, corresponding 
to the anterior third of the scapulae. At 4" 3", when the web was first looked 
at, the artery was contracted to absolute closure, and the web exsanguine ; 
and this state of things continued till 4 7™, when the vessel began to dilate. 
At 4 8m it measured 24°, and at 4) 13™, 3°. Four minutes later it was short 
of 3°, and after five minutes more it was observed to be undergoing spontaneous 
variations of calibre from 23° to 22°. Finally, at 54 30™ its condition was 
just as it was before the experiment was performed, varying from 14° to 2°, 
without any struggle on the part of the creature, the blood at the same time 
flowing rapidly through it.1. At 64, another vertebral arch having been taken 
away, the subjacent portion of cord was removed, the canal being thus cleared 
as far back as the level of the mid-scapulae, corresponding to rather more than 
a quarter of the cord. The operation caused contraction of the artery to 1°; 
but this passed off in half a minute, and was followed by no further dilata- 
tion than to 14°, and a few minutes later the artery was again spontaneously 
varying from 1° to 14°; at the same time the heart’s action was somewhat 
enfeebled. At 65 15™ the portion of cord corresponding to another vertebral 
arch was cut away. The operation induced contraction from 14° to 3°, 
followed by gradual dilatation (in fifteen seconds) up to 12°, and this, in a few 
seconds, gave place to spontaneous contraction to 13°. By this last operation 
the vertebral canal had been cleared as far back as the posterior third of the 
scapulae, corresponding to between one-third and one-half of the length of the cord. 
At 6h 30™, having removed another vertebral arch, I divided the cord 
imperfectly, as far back as it was exposed, namely, at the level of the posterior 
edges of the scapulae, which is in the commencement of the posterior half of the 
cord ; and on looking at the web twenty seconds later, found the artery under- 
going oscillations in calibre, such as had never before been seen in it, contracting 
and dilating distinctly five times in a minute, from 1° to 14° or 14°. At 62 32m 208 
the cord was cut fairly through at the point indicated, without removal of the 
segment from the canal, and at 64 34™ the artery was found quite constricted 
and the web exsanguine. At 6h 36™ ros the artery had somewhat dilated, and 
measured 14°, but the blood was moving very slowly through the vessels, the 
heart being exceedingly enfeebled. At 6 40™ the portion of the cord was 
* The transient character of the effects produced upon the arterial calibre by these operations 
led me at first to conclude that the anterior parts of the cerebro-spinal axis did not contain any nervous 
centre for the arteries, and this view was expressed in the original manuscript. My opinions on this 
point have, however, been altered by the results of subsequent experiments, as will appear at the con- 
clusion of the paper. 
