174 AIR AND LIFE. 



our body of this substance, which is unceasingly generated in our 

 tissues. It is not fit for breathing purposes, and all animals and plants 

 perish in a confined atmosphere when the proportion of this gas rises 

 above a very limited ratio. An atmosphere which contains one per cent 

 carbon dioxide has evil effects upon most organisms, and when the 

 ratio is ten per cent, life is endangered and death only a matter of time. 

 Carbonic acid is of no use at all to the tissues, and when we breathe 

 in an atmosphere where this gas is abundant, the blood corpuscles are 

 not able, in the lungs, to get rid of the carbon dioxide they have col- 

 lected in the body ; so they keep it, and, keeping it, they can not take 

 with them the amount of oxygen necessary for the cells and tissues. 

 It may be asked why they keep the former. The reason is that gas 

 exchanges between the blood and the atmosphere depend upon the 

 amount or tension of the gas in both media. As soon as the tension of 

 carbonic acid in the atmosphere is greater than that of the same gas 

 in the blood, the blood corpuscles retain their carbonic acid. If the 

 amount of carbonic acid in the atmosphere is increased, its tension 

 becomes at some point superior to that of the same gas in the blood 

 corpuscles. These, then, retain the noxious gas which takes the place 

 which should be abandoned to oxygen. The result is death by 

 asphyxia. Before death supervenes a condition of anaethesia is induced, 

 which Bichat specially investigated by means of an ingenious experi- 

 ment, through which the venous blood — well provided with carbonic 

 acid, of course — of one animal was made to pass into the carotid and cer- 

 ebral arteries of another, so that the latter had its brain irrigated with 

 asphyxic blood, and was brought to a condition of anaesthesia. Even 

 when applied locally to the surface of the skin, carbon dioxide induces 

 a state of local and temporary insensibility, a fact which seems to have 

 been long known and frequently utilized. Pliny relates in his Natural 

 History that marble (carbonate of lime), when mixed with vinegar and 

 placed upon the skin, puts the latter to sleep, i. e., renders it insensible, 

 so that it may be cut and burned without inducing pain. In this case 

 the anaesthetic agent is carbon dioxide, which is set free by the action 

 of the acetic acid of the vinegar upon the carbonate of lime. 



When carbon dioxide acts upon the entire organism, as when it is 

 inhaled by the lungs, it induces general anaesthesia. This has been 

 investigated by a number of physiologists, and one among them, M. 

 Ozanam, has found it so satisfactory that he feels no hesitation in 

 commending it as a substitute for ether or chloroform. His advice has 

 never, to my knowledge, been followed by surgeons or physiologists, 

 and some doubt may be expressed as to the expediency of using for 

 surgical or other purposes so dangerous an agent. Some cases are 

 known in which man has been deeply under the influence of carbon 

 dioxide without fatal results. In such circumstances, anaesthesia has 

 been complete. The patients relate, at least some of them, that before 

 becoming unconscious there occurs a delightful condition during which 



