ficial forms of lethargy, the premonitory stages of anæsthesia only are approximate in character to normal sleep. Nitrous oxide, with oxygen, is now largely administered to the point of insensibility, by distinguished physicians, to produce vicarious sleep, in cases of obstinate insomnia, and is regarded as a priceless remedy. But the lethargy thus produced is dreamless, and therefore not normal sleep. The mental and moral natures of the individual are in a condition of suspended animation, which, from what has been previously set forth, is an abnormally torpid condition of life. Further, it has been shown that complete anæsthesia itself differs essentially from natural sleep; for in the latter the senses are only dulled, and still remain more or less susceptible to strong external impressions, by dint of which wakefulness is readily brought about.
The question now arises, Is there any agent which exerts in small doses a sedative effect on both body and mind, an effect that increases with the dose or with the period of action, until entire insensibility finally results, and which, like nitrous oxide, works no permanent harm? The answer is that we have one such agent, carbon dioxide gas; itself a constant and copious product of normal animal life.
It is placed by Richardson, an eminent specialist on this subject, among anæsthetics, and this place is generally conceded to it. Even in the day of Pliny, its outward effects were familiarly known, as at the Grotta del Cane, near Naples. Popularly it is deemed a deadly poison, but many chemists have held that it is not so. In mines and deep wells it is usually unmixed with air, and the result of inhalation is, of course, speedy suffocation. Berzelius long ago stated that air containing five per cent can be breathed without serious injury. Dr. Angus Smith found, nevertheless, that one twenty-fifth of this proportion produced a slow diminution of the circulation, such as we have seen accompanies natural sleep. We have one experiment made by a commission on coal mines of the British Association, in which an animal exposed to carbon dioxide and air, half and half, a small jet of air being, however, continuously introduced to maintain a supply of free oxygen, lived "for a long time"—how long not stated. Here, plainly, rapid poisonous action is shown to be absent.[1]
- ↑ New facts have appeared since the above was written that add great strength to the positions taken here against the generally assumed highly toxical qualities of carbon dioxide—a body always present in the lungs and blood of men and animals. The experiments of Berzelius above cited—like all others of that unparalleled chemical genius—as to the toleration of animal life for important amounts of this supposed poison, stand now as being much more than verified. To wit, among others, an English experimenter, Mr. T. H. Wilson, has found that rabbits are uninjured by breathing for an hour air containing twenty-five per cent of the much-dreaded gas. At the last meeting of the British Association, Dr. J. S.
