373 COMBUSTION OF CARBON. 



From these sums it appears that the azote of the excrements is 

 less by from 339.6 to 455.0 grains than that of the forage consumed. 

 It appears also that the whole q. antity of elementary matter con- 

 tained in the excrements is less than that which had been taken as 

 food ; the difference is of course due to the quantities which were 

 lost by respiration and the cutaneous exhalation. 



The oxygen and hydrogen that are- not accounted for in the sum 

 of the products have not disappeared in the precise, proportions re- 

 quisite to form water ; the excess of hydrogen amounts to as many 

 as from 13 to 15 dwts. It is probable that this hydrogen of the 

 food became changed into water by combining during respiration 

 with the oxygen of the air. 



The loss of carbon, which is very considerable, seeing that in the 

 two experiments it asiounts to nearly 12^ lbs., must have gone to 

 form the carbonic acid, which is known to be so large and import- 

 ant a constituent in the expired air, and which is also exhaled iVorn 

 the general surface of the body. Neglecting the latter, it appears 

 that each of the animals produced in the course of twenty-four 

 hours upwards of 13 cubic feet of carbonic acid gas, the thermome- 

 ter supposed at 32*^ F., the barometer at 30 inches.* 



During respiration, then, or as a consequence of respiration, the 

 carbon and hydrogen of the food have disappeared and given rise, 

 by the concurrence of the oxygen of the air, to carbonic acid and 

 water, precisely as if they had been burned. And an animal may, 

 in fact, be regarded as an apparatus or system, in wliich a slow com- 

 bustion is incessantly going on ; there is perpetual disengagement 

 of carbonic acid gas and of the vapor of water, just as there is from 

 a stove in which any organic substance, wood, for example, is burn- 

 ing. In either case there is evolution of heat ; all animals have a 

 temperature above that of the medium which surrounds them, and 

 the excess of the elevation is in some sort relative to the activity of 

 the respiratory process, or, in other words, to the intensity of the 

 combustion. 



Under the influence of the oxygen that is taken into the body, the 

 soluble principles of the blood pass through a series of modifications, 

 the last of which is carbonic acid, which is exhaled and dissipated 

 in the air ; and it is in this way that a portion of the carbon of the 

 food is returned to the atmosphere, after having accomplished the 

 important function of supplying the animal with the heal that is ne- 

 cessary to its existence. Far from deriving any thing from the air, 

 consequently, animals, on the contrary, are continually pouring car- 

 bon into it. The tbod is, therefore, the only source whence animals 

 derive the matter that enters into their constitution ; and, as the 

 primary food of animals is obtained from vegetables, herbivorous 

 creatures must necessarily find in the plants they consume all the 



• The large qimntity of carbonic acid shows the necessity for laree and well-venti- 

 lated stable-* iiiul cow-houses. A cow, i' appears, will vitiate 66 cubic feet of air In 

 a day. It will b ' observed in the tJible tliat the saline and earthy nmttcrs of thd 

 ejecta exceed those of the ingesta in both instances. This is from error in observa 

 tion, and is owing to the difficulty of dUermining exactly the quantities of these sub 

 stances. I'he error is less in the case f the horse than .n that of the cow. 



