On chloroform and other anæsthetics: their action and administration

by John Snow

Experiment 50. Fifty grains of amylene were diffused in a glass jar holding 330 cubic inches, and a linnet was introduced by momentarily moving the lid a little to one side. It was quickly affected, and in about a quarter of a minute was lying quite insensible. It remained so, breathing quickly and naturally, and made no effort whatever when rolled about in the jar. It was allowed to remain three minutes, and there was a slight fluttering motion of the wings just before its removal. It was quite passive when removed, and insensible to pricking of the soft part of the foot. It began to recover its sensibility in three-quarters of a minute. In two minutes it was able to stand, and in six minutes it got on the perch. There was twenty per cent. of vapour in the air in this experiment.

As amylene boils nearly at the temperature of the blood, that fluid would be able to absorb about one-fifth as much as it would be able to dissolve, when an atmosphere is breathed containing twenty per cent. of the vapour, which produces a complete state of insensibility, or the fourth degree of narcotism. When ten per cent. is breathed, which has been shown to cause the second degree of narcotism, about one-tenth as much vapour as the blood would dissolve must be absorbed. In treating of chloroform and ether, it was previously shewn that the fourth degree of narcotism was caused by one twenty-eighth part as much of these agents as the blood would absorb; and the second degree by one fifty-sixth part. And these were the proportions absorbed of several other agents which are made from ordinary alcohol, and will afterwards be mentioned.

Although the proportion of amylene absorbed is large in relation to the whole quantity which the blood would dissolve, it is a very small amount on account of the extremely slight solubility of the agent. If we estimate the average amount of serum of the blood in the human adult at 410 fluid ounces, as before, then, as amylene requires 9,319 parts of watery fluids for its solution (as nearly as I could ascertain), the quantity of this agent in the system must be rather less than three grains in the fourth degree of narcotism; rather less than a grain and a half in the second degree; and a very little over two grains in the third degree of narcotism, the condition in which surgical operations are usually performed. Amylene is therefore, when absorbed, about as powerful in its medicinal properties as the alkaloids.

The following fact also proves that but a very small quantity of amylene is absorbed. In breathing this agent backwards and forwards from a small bladder containing 200 cubic inches of air, fourteen minims was the largest quantity I could put into the bladder without being rendered unconscious; but in employing a large bladder holding 670 cubic inches, I could put in forty-five minims, and breathe it backwards and forwards for some time without being rendered unconscious. With fifty minims of amylene I immediately forgot where I was; but awoke in a minute or two, seated in the same position, and with the bladder in my hand. Fifty minims of amylene would produce between six and seven per cent. of vapour in the bladder; and after the air in the lungs became mixed with that in the bladder, there would be rather more than five per cent. of vapour in it.

Viewed in the light of the small quantity which requires to be absorbed into the system to cause insensibility, amylene is a very powerful agent; but when considered in relation to the quantity which is consumed during inhalation in the ordinary way, it is very far from being powerful. This arises from the great tension and the small solubility of the vapour, in consequence of which it is, with the exception of a small fraction, expelled from the lungs again without being absorbed. In this respect it resembles, to a great extent, the nitrogen gas of the atmosphere, with which the lungs are always four-fifths filled, while the blood contains but a few cubic inches. It takes from three to four fluid drachms of amylene to cause insensibility in the adult.

I found, by my experiments on animals, that amylene is, like chloroform and some other agents, capable of causing sudden death by over-narcotism of the heart, and paralysis of that organ; but that it is more difficult to cause this kind of sudden death with amylene than with chloroform.

Experiment 51. One hundred and twenty grains of amylene were made to evaporate in a jar holding 330 cubic inches, and a full grown guinea pig was suddenly introduced, the cover being partly removed for a moment. It was allowed to remain for about a minute, when the breathing became of a gasping character. Being taken out, and the stethoscope applied immediately to the chest, the heart could not be heard to beat; and its action did not return, although the gasping continued for about a minute. There was nearly 48 per cent. of vapour in the air in this experiment, except that a small quantity might escape as the guinea pig was introduced. I had tried guinea pigs with smaller proportions of vapour in the air, but had not succeeded in arresting the action of the heart.

The lungs were rather congested, and the right cavities of the heart were filled, and somewhat distended with coagulated blood.

Experiment 52. A kitten, six weeks old, was placed in a jar holding 330 cubic inches, after ninety-five grains of amylene had been made to evaporate and diffuse itself. The kitten remained three-quarters of a minute in the jar, and was suddenly taken out. It was scarcely insensible on its removal, but soon became so. The stethoscope was applied, and the heart was found to be beating rapidly. The kitten quickly recovered.

One hundred and six grains of amylene were made to evaporate in the same jar, and the kitten was quickly introduced, as before, by moving the cover for a moment. It was allowed to remain for half a minute, and removed with the same symptoms and result as before.