"Administration of chloroform"

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[The PDF contains Mr. Witten's second letter on the subject, in which he expressed dissatisfaction with

Snow's first explanation of why he had failed to render a patient insensible. The PDF also contains Snow's extended reply, transcribed below.]

To the Editor of the Medical Times and Gazette.

Sir,--I consider that the time over which the inhalation extended in Mr. Witten's case of administration of chloroform explains the want of success, when we take into account the circumstance, that with the form of inhaler which he used only a part of the chloroform is taken into the lungs, and that a great portion is blown away by the warm breath during expiration. Mr. Witten would probably say that he has succeeded in other cases when using the same inhaler, apparently in the same manner. But the effect produced depends entirely on the proportion of chloroform vapour in the air breathed by the patient, and this varies, in using such an inhaler, with a number of circumstances which may easily pass unobserved; as, the accuracy with which the inhaler fits the face, the temperature of the sponge, and the amount of air which passes through it before being breathed. I have not found that the nervous temperament has rendered patients less susceptible to the influence of chloroform, and, as regards the deterioration of the blood, no amount of it which is consistent with life could affect the absorption of the vapour in the lungs, which is a strictly physical process.

With respect to my statement, that twelve minims of chloroform, when present in the blood, causes unconsciousness, I am able to adduce not only a calculation, but a direct experiment, in proof of it. The calculation is founded on some experiments which I published in the Medical Gazette for 1848, Vol. I. I found, that when animals were made to breathe air containing as much vapour of chloroform as would enable the blood to take up one fifty-sixth part, as much as it is capable of absorbing, it produced what I call the second degree of narcotism; a state in which the animals were incapable of perceiving what was occurring around them. Now, the serum of the blood, like other watery fluids, is only capable of dissolving about one part in 288 of its volume of chloroform; and if this number be multiplied by 56, and the quantity of serum in the body, (which, according to the experiment of Valentin, averages 410 fluid ounces,) be divided by the product, the result is 12 minims. The direct experiment is as follows:--If 12 minims of chloroform be put into a good-sized bladder, with 400 to 500 cubic inches of air, and an adult person breathes it backwards and forwards, as he would breathe laughing gas, he becomes quite unconscious in less than a minute; not sufficiently insensible for a surgical operation--for that would require about 18 minims--but he becomes altogether oblivious of everything about him. It is not necessary or desirable to exhaust the lungs before performing this experiment. The 12 minims of chloroform are undoubtedly diffused through the blood of the whole body. When animals are killed with chloroform I can detect it by chemical analysis as easily in the muscles as in the brain, and I found it readily in the leg of a hog, which was amputated while he was under the influence of the vapour. The quantity of chloroform in the brain at any one time is much less than a single minim, but this need not surprise us when we know in what small quantities the alkaloids produce their effects. Chloroform appears to produce its effects without undergoing any change itself; for, after a person has inhaled it, the vapour may be detected by chemical tests coming off unchanged in the breath; it can be detected in the bodies of animals killed by it, for a fortnight after death; and, lastly, by breathing it, mixed with oxygen, from a bladder, and making an arrangement to absorb the carbonic acid produced, the effect of a small quantity may be kept up for an indefinite period, and a few minims can be made to do the work of several drachms.

I am, etc.

John Snow, M.D.

18, Sackville-street, June.