In the course of many investigations into the action of drugs on animals it is necessary to perform experiments which would be painful unless the animals were anaesthetised. The easiest way of doing this with frogs or small animals, such as mice, rats, or rabbits, is to put them under a bell-jar with an opening at the top. Into this opening a piece of cotton-wool or blotting-paper is put, and chloroform dropped on it. The vapour being heavier than air falls to the bottom, and the animal soon becomes insensible. The best way of anaesthetising cats, small dogs, or very large rabbits, is to put them into a wooden box or tin pail, and stretch a towel tightly over the top. An assistant then pours some chloroform on the towel and anaesthesia is quickly produced. Rats are most readily anaesthetised by completely covering the cage, in which they are, with a towel, and dropping chloroform upon it.

Rabbits may be very quickly anaesthetised by the plan employed by Pasteur. It consists in putting a piece of cloth or blotting-paper soaked in chloroform round the animal's nose so as to exclude air. At once the rabbit ceases to breathe, and remains without breathing for about a minute. It then begins to struggle, and if the anaesthetic be kept closely applied the respiratory movements shortly become steady and regular and the animal completely insensible.

For very large or savage dogs an old packing-case without a lid may be simply placed over the animal and held firmly down, or one of the sides may be furnished with hinges so as to convert the case into a sort of kennel. After the dog is safely housed large pieces of blotting-paper or of cloth on which chloroform is poured are pushed through cracks in the top of the case or holes specially made for the purpose. The outer ends of the blotting-paper or cloth remaining outside, fresh quantities of chloroform can be introduced as required until complete anaesthesia is produced. Anaesthesia may be maintained for almost any length of time that is required, by putting a piece of cloth loosely round the animal's nose and dropping chloroform upon it. This requires careful attention, however, in order to prevent danger from an overdose on the one hand, or partial recovery on the other. I find the most convenient way of maintaining the anaesthesia induced by chloroform in the way already mentioned is to put a cannula in the trachea and connect it with a flask containing ether, so that the inspired air passes over the surface of the ether, and carries a quantity of the vapour with it into the lungs of the animal. By means of a peculiar stopcock, the construction of which is indicated in the diagram (Fig. 73), pure air or air loaded with ether vapour or a mixture of both may be given.

The advantages of employing this method and of using ether rather than chloroform are that complete anaesthesia may be kept up for hours together with little or no attention on the part of the operator, and without the respiration or blood-pressure being seriously affected by the anaesthetic.

Fig. 73.   Diagram of a stopcock by which air or vapour, or two kinds of gas, may be given alone, or mixed together in any proportion.

Fig. 73. - Diagram of a stopcock by which air or vapour, or two kinds of gas, may be given alone, or mixed together in any proportion.

Another plan of maintaining anaesthesia for a length of time is to inject some laudanum or liquid extract of opium into a vein after anaesthesia has been induced by chloroform. Before the effect of the chloroform has passed off, such complete narcosis is produced by the opium that no procedure, however painful it might otherwise be, will produce the slightest evidence of sensation. When the effect of the anaesthetic or of the opium would interfere with the investigation of the action of a drug on the circulation or reflex action, the animal may be anaesthetised by chloroform, and the crura cerebri divided. The channels by which painful impressions are conveyed to the brain being thus destroyed no pain can be felt, although the reflex action of the cord again returns after the effects of the chloroform have passed off.

History of the Discovery of Anaesthesia

This is a subject of considerable interest, and has given rise to much discussion. The starting-point of the discovery seems to have been Sir Humphry Davy's observations on the properties of nitrous oxide, regarding which he said, 'as nitrous oxide in its extensive operation seems capable of destroying physical pain, it may probably be used with advantage during surgical operations.' The property of this gas and also of ether vapour to produce excitement when inhaled, caused these substances to be used in sport, and during their action bruises were frequently received, but not felt. This circumstance excited the attention of Dr. Crawford W. Long, of Athens, Georgia, and, in 1842, he anaesthetised a patient with ether in order to remove a tumour. He was encouraged to do this by the fact that Dr. Wilhite, in a frolic, had rendered a negro boy completely insensible without any bad results. Mr. Horace Wells, without knowing what Dr. Long had done, used nitrous oxide as an anaesthetic in 1844. His pupil, Mr. Morton, wishing to use it also, asked him how to make it, and was referred to a scientific chemist, Dr. Jackson. Jackson advised Morton to use sulphuric ether, as it had similar properties to nitrous oxide and was easier to get. Acting on this suggestion Morton used ether in dentistry, and induced Drs. Warren, Haywood, and Bigelow to perform important surgical operations on patients whom he anaesthetised by it. From this time onwards anaesthesia has been regularly used in medical operations. Shortly afterwards, Sir J. Y. Simpson discovered the use of chloroform as an anaesthetic, and it has been chiefly employed in Great Britain, but in America ether has always retained its original place.