EFFECTS OF FOREIGN GASES. 847 



be considered, as well as the great influence of atmospheric moisture, 

 in increasing the exhalation of carbonic acid, and of a dry air in di- 

 minishing it. It is possible that, in some degree, the hygienic value 

 of a dry climate, such as Egypt, in the treatment of diseases of ex- 

 haustion, may depend upon the comparatively limited amount of waste 

 and oxidation of the tissues generally. 



In hibernating animals, the quantity of oxygen absorbed and car- 

 bonic acid evolved is, like the respiratory movements themselves, re- 

 duced to a minimum, or, it is said, the respiratory interchanges are 

 even absolutely arrested. 



i 



Effects of Breathing other Grases than Air. 



As already mentioned, many gases and vapors of volatile substances 

 are introduced into the system by absorption from the pulmonary mu- 

 cous membrane. Chloroform, ether, camphor, and turpentine, thus 

 produce their characteristic active results on the system ; so likewise 

 do tobacco smoke, the smoke of the datura stramonium, and the vapor 

 of mercury. The gaseous combinations of hydrogen, with other ele- 

 ments, such as arseniuretted, phosphuretted, sulphuretted, and car- 

 buretted hydrogen, are especially and directly poisonous. The arsen- 

 iuretted hydrogen is the most powerful, less than one-tenth of a grain, 

 when inhaled, having proved fatal to Man. Sulphuretted hydrogen 

 stands next in potency, air containing from one to three per cent, 

 having been respired without much inconvenience to Man, though much 

 less destroys animals. Carburetted hydrogen, or marsh-gas, the fire- 

 damp found in coal mines, is still less active as a poison, but destroys 

 life when present in large proportions. The vapors of nitric, nitrous, 

 sulphurous, and hydrochloric acids, as well as those of ammonia, 

 which are compound bodies, and those of bromine, iodine, and chlo- 

 rine, which are simple bodies, are likewise positively injurious when 

 inhaled into the lungs, causing direct irritation of the mucous mem- 

 brane, and producing decompositions of a special kind when taken 

 into the blood. Besides causing an increase of the mucous secretion, 

 intense bronchorrhoea, serous inflammation, and often permanent 

 cough, they frequently produce, through reflex nervous action, violent 

 spasm of the glottis, and so may cause asphyxia or death from suffo- 

 cation, without entering the air- tubes; sometimes death results from' 

 oedema of the glottis. There is one gas, a compound of nitrogen with 

 oxygen, the nitric oxide, or laughing gas, which, when inhaled for 

 some minutes, produces a state of temporary intoxication, and, at the 

 same time, maintains respiratory chemical changes at the expense of 

 the oxygen contained in it, the products of respiration being, in such 

 a case, carbonic acid with a large excess of nitrogen. By a long con- 

 tinuance of the experiment, insensibility, and, as has been shown on 

 animals, actual suffocation, probably from the carbonic acid, may be 

 produced. 



Besides these directly irritant and poisonous gases, there are some 

 which are only indirectly injurious, being in themselves inert and in- 

 nocuous. Thus, snails have been kept in pure hydrogen for a long 



