382 OF RESPIRATION. 



ments, and, when sufficiently powerful, in their complete suspension. 

 Under such circumstances, it is requisite to resort to all possible means 

 of keeping up the respiratory movements ; and when these fail, arti- 

 ficial respiration may be successfully employed. For if, by such 

 means, the circulation can be prevented from failing for a sufficient 

 length of time, the ordinary processes of nutrition go on, the poisonous 

 matter is gradually decomposed, or eliminated by the secreting organs ; 

 and the nervous centres resume their usual functions. A torpid con- 

 dition of the medulla oblongata, inducing a retardation of the respira- 

 tory movements, seems to be one of the morbid conditions attendant 

 upon typhoid fever ; and probably depends in the first instance upon a 

 disordered state of the blood, which does not exert its usual vivifying 

 influence. In such cases, the proportion of the respiratory movements 

 to the pulse sinks as low as 1 to 6, or even as 1 to 8 ; and thus the 

 due aeration of the blood is not performed, and its stimulating proper- 

 ties are still further diminished. 



4. Chemical Phenomena of Respiration. 



689. Having now fully considered the means, by which the Atmo- 

 sphere and the Blood are brought into relation in the lungs, we have 

 to examine into the results of their mutual action. It will be remem- 

 bered that the Atmosphere contains about 21 per cent, of Oxygen to 

 79 of Nitrogen, by measure ; or 23 parts of Oxygen to 77 of Nitrogen, 

 by weight. The changes which it undergoes in Respiration may be 

 considered under four heads : 1. The disappearance of Oxygen, which 

 is absorbed. 2. The presence of Carbonic Acid, which has been exhaled. 

 3. The absorption of Nitrogen. 4. The exhalation of Nitrogen. Of 

 these, the first two are by far the most important. It was formerly 

 supposed that the Oxygen which disappears, is the precise equivalent 

 of the Carbonic Acid which is set free (the latter gas containing its 

 own bulk of the former) ; and that the union of the absorbed oxygen 

 with the carbon to be eliminated, takes place in the lungs. It is now 

 known, however, that the carbonic acid is given out ready formed, its 

 production having taken place at the expense of oxygen previously 

 contained in the blood ; and that a much larger proportion of oxygen is 

 usually absorbed, than is contained in the carbonic acid exhaled, the 

 difference sometimes exceeding the third,, part of the carbonic acid 

 formed, whilst it is sometimes so Small that it may be disregarded. 

 This diversity seems to depend, partly upon the constitution of the 

 species experimented on, and partly upon the degree of development of 

 the individual, but in great part upon the nature of the food ; it having 

 been established by the recent experiments of MM. Regnault and 

 Reiset, that the quantity of oxygen absorbed into the system is much 

 greater on an animal diet, than on a farinaceous. It is certain that, of 

 this absorbed oxygen, a part must enter into combination with the sul- 

 phur and phosphorus of the original components of the body, converting 

 these into sulphuric and phosphoric acids ; and the remainder must enter 

 into other chemical combinations, very probably uniting with the hydro- 



