182 REPORT—1868, 
when very dangerous agents are in daily use, has never, as far as I know, 
happened. 
In searching for the agents we require, we must begin by excluding bad 
ones, which is, in fact, to exclude whole classes. The class of the chlorides, 
under this rule, would all go. It is true they are not all equally dangerous, 
and that the increase of danger is in proportion to the substitution of chlo- 
rine; but, asa class, they one and all do more than we require, they produce 
muscular rigidity, vomiting, and decrease of animal heat. This same rule holds 
good in relation to the iodides and the bromides. Supposing, then, we keep to 
the methyi and ethyl series as bases, we are driven back to the oxides, to what 
are commonly the ethers, for our agents. None of these which have yet been 
applied have been actually perfect ; but it is almost certain that in course of 
time the chemist will produce for the physiologist the precise requirement. 
That it may be generally known what this requirement is, I will state in a 
few sentences the theoretical formula of a safe anesthetic, an anesthetic 
that shall be applicable to long and short operations alike, and shall become 
acceptable generally from its readiness and safety. 
1. It must be a fluid. Gases, however good, are not practicable as agents 
for general and daily use; more than this, as at the temperature of the blood 
they remain as gases, and when dissolved in blood they exert no action from 
change of form in the organism. ‘To narcotize with them it is consequently 
necessary to give them in large quantities, even it may be to the exclusion 
of air altogether. The influence of a gas thus administered is of necessity 
limited to the briefest interval of time; steady continuance would lead to 
certain death from asphyxia. 
2. The fluid must possess homogeny and stability. Mixtures of fluids are 
utterly unreliable. Fluids which easily decompose under the influence of 
heat or of light are unreliable. 
3. The fluid must be of pleasant odour, and must produce no irritation 
when inhaled or when applied to the skin. All the fluids which, like chloro- 
form, amylene, and turpentine, cause redness and irritation of skin, cause 
also, when introduced into the blood, irritability of muscle and rigidity, toge- 
ther with vomiting. 
4, The boiling-point of the fluid should be not less than 110° Fahr., and 
not over 130°. Fluids which pass into vapour below the temperature of the 
animal body act practically as gases, and must be used in free quantities to 
the exclusion of air ; common ether, amylene, and bichloride of methylene have 
this fault, the last least. Fluids, on the other hand, which pass altogether 
into vapour at a point much above the animal temperature, as at 140° or 
upwards, condense in the pulmonary blood too determinately, and although 
they create a long sleep, they remain for a considerable period in the body, 
creating continued nausea and depression from interference with the conser- 
vation of the animal heat. Chloroform, tetrachloride of carbon, and common 
alcohol are objectionable on these grounds. A fluid which should have a 
boiling-point some 20° above the body, and other properties equally good to 
commend it, would be convenient in every respect. It could be easily preserved, 
and as an anesthetic it would be alike applicable to long and short operations, 
5. The density of the vapour of the fluid should be about 40, taking 
hydrogen as unity. 
In the large Table before the Section I have named a list of substances 
(23 in all), which have received from me the most careful investigation ; 
they are all wanting in some property that is essential, but one or two new 
observations respecting the action of certain of them are worthy of notice. 
