." (18,677)[1]

[1] Figures in parentheses refer to the questions or replies in the
printed evidence.

"Supposing you were giving chloroform with CURARE, then it might be
said you were not giving enough chloroform. BUT YOU CAN SEE WHETHER
YOU ARE GIVING ENOUGH BY LOOKING AT THE BLOOD-PRESSURE." (18,690)
Professor Dixon tells us that one of the gauges used for determining
whether anaesthesia is present or not IS THE BLOOD-PRESSURE. "The
blood-pressure goes DOWN BECAUSE THE CHLOROFORM IS GIVEN. The heart
beats more feebly; therefore the blood-pressure goes down." (18,742)

Another expert physiologist, whose testimony on this point is
enlightening, was Dr. Eh. H. Starling, professor of physiology at
University College, London.

"Are there any means, other than the cries or struggles of the animal,
by which you can tell whether the anaesthetic is passing off?"

"YES, YOU CAN TELL IT BY THE BLOOD-PRESSURE," Dr. Starling
replied. "When one is working without curare, one notices THAT THE
PRESSURE GOES UP, and then, if one does not attend to it, after that
comes a little movement, AND YOU GIVE MORE ANAESTHETIC." (4,054)

We need not follow Professor Starling in his repeated assurances of
complete anaesthesia in his vivisections; all this is merely an
expression of faith in the accurate and perfect working of his
instruments, a faith which some of the Commissioners did not share.
What interests us is the statement that IF THE ANAESTHESIA IS
IMPERFECT, THE BLOOD-PRESSURE WILL REVEAL IT. "The pressure goes up";
there is some slight motion on the part of the animal; IT FEELS, and
that returning sensibility to painful impressions is indicated by an
increase in the pressure of the blood.[1]

[1] Sir Victor Horsley admitted that "changes in the blood-pressure"
afford an indication whether anaesthesia is perfect or not
(Ques. 16,057).

But how is the measurement of the blood-pressure to be ascertained?
One of the instruments in use is thus described:

"The pressure exerted upon the blood in the arterial system may be
measured by attaching the carotid artery of a living animal to a
reservoir of mercury, provided with an upright open tube or pressure-
gauge.... Under pressure of the blood, the mercury rises in this tube,
and the height of the mercurial column becomes an indication of the
pressure to which the blood itself is subjected within the artery.
The arterial pressure is found to be equal to the average of a column
o