238 THE POPULAR SCIENCE MONTHLY. 



ficial forms of lethargy, the premonitory stages of anaesthesia 

 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 price- 

 less 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 an- 

 aesthesia 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, carhon dioxide gas ; itself a constant and copious iwod- 

 iict of normal animal life. 



It is placed by Richardson, an eminent specialist on this sub- 

 ject, among anaesthetics, and this place is generally conceded to 

 it. Even in the day of Pliny, its outward effects were familiarly 

 known, as at the Orotta 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, never- 

 theless, 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 ex- 

 posed 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.* 



* 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 tolera- 

 tion 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. 



