AXIMAL HKAT. 259 



the oxidation of their carbon and hydrogen, and immediately ex- 

 pelled from the body without ever having formed a part of the solid 

 tissues. He therefore divided the food into two different classes of 

 alimentary substances ; viz., 1st, the nitrogenous or plastic elements, 

 which are introduced in comparatively small quantity, and which 

 are to be actually converted into the substance of the tissues, such as 

 albumen, muscular flesh, &c.; and 2d, the hydro-carbons or respiratory 

 elements, such as sugar, starch, and fat ; which, according to his view, 

 are taken into the blood solely to be burned, never being assimilated 

 or converted into the tissues, but only oxidized in the circulation, 

 and immediately expelled, as above, under the form of carbonic 

 acid and water. He therefore regarded these elements of the food 

 only as so much fuel ; destined simply to maintain the heat of the 

 body, but taking no part in the proper function of nutrition. 



The above theory of animal heat has been very generally adopted 

 and acknowledged by the medical profession until within a recent 

 period. A few years ago, however, some of its deficiencies and 

 inconsistencies were pointed out, by Lehmann in Germany, and by 

 Eobin and Yerdeil in France ; and since that time it has begun to 

 lose ground and give place to a different mode of explanation, more 

 in accordance with the present state of physiological science. We 

 believe it, in fact, to be altogether erroneous; and incapable of 

 explaining, in a satisfactory manner, the phenomena of animal heat, 

 as exhibited by the living body. We shall now proceed to pass in 

 review the principal objections to the theory of combustion, con- 

 sidered as a physiological doctrine. 



I. It is not at all necessary to regard the evolution of heat as 

 dependent solely on direct oxidation. This is only one of its 

 sources, as we see constantly in external nature. The sun's rays, 

 mechanical friction, electric currents, and more particularly a great 

 variety of chemical actions, such as various saline combinations and 

 decompositions, are all capable of producing heat; and even simple 

 solutions, such as the solution of caustic potassa in water, the mixture 

 of sulphuric acid and water, or of alcohol and water, will often pro- 

 duce a very sensible elevation of temperature. Now we know that 

 in the interior of the body a thousand different actions of this 

 nature are constantly going on ; solutions, combinations and decom- 

 positions in endless variety, all of which, taken together, are amply 

 sufficient to account for the production of animal heat, provided the 

 theory of combustion should be found insufficient or improbable. 



