Dr. W. E. Dixon of King's College, London, representing one of the sections of the Royal Society of Medicine, gave evidence before the Royal Commission on various matters pertaining to anaesthesia. Dogs, he asserted, "very easily die of chloroform; but if one goes sufficiently slowly they never die." (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 of mercury 150 millimetres, or 6 inches, in height."