824 SPECIAL PHYSIOLOGY. 



nitrogen appears to be given off into the expired air. Lastly, owing 

 to the excess of oxygen absorbed over the carbonic acid exhaled, there 

 is a loss of 1 per cent, of the air inspired. These results are founded 

 on nearly 600 observations ; but, as we shall hereafter see, individual 

 experiments exhibit remarkable deviations, according to numerous 

 circumstances. 



Absorption of Oxygen. The quantity of oxygen absorbed in respi- 

 ration is determined by careful examination of the quantity left in the 

 expired air. This is done by using pyrogallic acid, which greedily 

 attracts it, to take it up, or by combining it with hydrogen by means 

 of the electric spark. There is no doubt that the greater portion of 

 the oxygen absorbed, which in a single respiration is about Jth the total 

 quantity in the air, combines somewhere, and in some way, with car- 

 bon, to form the carbonic acid which is exhaled. But as the carbonic 

 acid produced exactly equals in volume the oxygen concerned in its 

 production, the surplus of oxygen absorbed over the carbonic acid ex- 

 haled must remain in the system, and is probably therein combined 

 with hydrogen, or with the sulphur and phosphorus of the albuminoid 

 constituents of the body. In Man, from ith to ^th of the total amount 

 of oxygen absorbed does not reappear in the carbonic acid, but remains 

 to be combined with other oxidizable substances. In dogs fed upon 

 carbhydrates, such as starch or sugar, or even upon milk, T 9 ths of the 

 oxygen absorbed are returned as carbonic acid, only y^th remaining 

 in the system ; if large quantities of flesh are eaten, more of the oxy- 

 gen, i. #., ith, is retained; lastly, when fat alone is consumed, T 3 oths 

 are retained, as if a pure fat diet stimulated the oxidation of the nitro- 

 genous tissues. (Regnault and Reiset.) Again, in Herbivorous ani- 

 mals which consume many carbhydrates in their food, the proportion 

 of oxygen retained in the system is exceedingly small ; whereas, in 

 Carnivorous animals, the food of which is chiefly nitrogenous, but also 

 fatty, a very large proportion is retained. (Dulong and Despretz.) 

 In starving animals also, which practically live carnivorously, i. e., on 

 their own tissues, a large proportion of the oxygen is retained, amount- 

 ing even to fths of the total quantity absorbed. 



Elimination of Carbonic Acid. : The fact of the elimination of this 

 gas from the lungs, may be shown by blowing slowly through a tube 

 into lime-water, which soon becomes turbid from the formation of 

 carbonate of lime, more especially as the last quantities of air are 

 being expelled from the chest. The determination of the quantity of 

 carbonic acid gas given off in respiration, is extremely difficult, not- 

 withstanding the ingenuity of the methods employed for this purpose. 



The simplest method, used by Prout, Dumas, Vierordt, and others, 

 consists in causing a person to inspire air through the nose, and ex- 

 pire it through a tube, held in the mouth, into a closed bag or receiver; 

 and then in analyzing the expirejd air, by agitation with lime-water or 

 with a solution of caustic potash, either of these substances absorbing 

 the carbonic acid, which can thus be measured. The oxygen has, at 

 the same time, been estimated, by means of pyrogallic acid, or by de- 

 flagration with hydrogen, by means of the electric spark. (Vierordt.) 

 Such a method, excellent for individual trials, is not adapted for gen- 



