SOURCES OF ANIMAL HEAT. 519 



The Consumption of Oxygen and Production of Carbonic Acid in Connection with 

 the Evolution of Heat. As far as it has been possible to determine by actual experi- 

 ment, all animals, even those lowest in the scale, appropriate oxygen and eliminate car- 

 bonic acid. This is equally true of all living tissues ; and, since it has been ascertained 

 that oxygen is dissolved, as oxygen, in the arterial blood, that it disappears in part or 

 entirely in the capillary circulation, that carbonic acid is taken up by the venous blood, 

 both in solution and in feeble combination in the bicarbonates, to be discharged in the 

 lungs by displacement and the action of the pneumic acid, and that the tissues them- 

 selves have the property of appropriating oxygen and exhaling carbonic acid, those who 

 adopt the theory of Lavoisier have simply changed the seat of oxidation from the lungs 

 to the general system. 



It has been proven beyond question that oxygen, of all the principles introduced from 

 without, is the one most immediately necessary to nutrition ; and it differs from the class 

 of substances ordinarily known as alimentary, only in the fact that it is consumed more 

 promptly and constantly. In the same way. carbonic acid is to be regarded as an ele- 

 ment of excretion, like urea, creatine, etc., differing from them only in the immediate 

 necessity for its elimination. As the comparatively slow excretion of urea and other 

 nitrogenized matters is connected with the ingestion of ordinary alimentary substances 

 that are slowly appropriated by the tissues, so the rapid elimination of carbonic acid is 

 connected with the equally rapid appropriation of oxygen. There is no reason why we 

 should not regard carbonic acid, like other effete substances, as an excretion, the result 

 of disassimilation of the tissues generally ; but, more closely than any, it is connected 

 with the rapid and constant evolution of heat. 



Experiments on the influence of the sympathetic nerves upon the temperature of par- 

 ticular parts have completed the chain of evidence in favor of the localization of the 

 heat-producing function in the tissues. It is not our purpose to discuss the relations of 

 the sympathetic system to nutrition, deferring this subject until we come to treat spe- 

 cially of the nervous system ; but the facts bearing on calorification are briefly as follows : 



If the sympathetic nerve be divided in the neck of a rabbit or any other warm- 

 blooded animal, the side of the head supplied by this nerve will become from five to 

 eight or ten degrees warmer than the opposite side, or than the rest of the body. This 

 observation we have repeatedly verified. The conditions under which this local exag- 

 geration of the animal heat is manifested are, dilatation of the arteries of supply of the 

 part, so that it receives very much more blood than before, and increased activity in the 

 general process of nutrition. It also has been observed, in experiments upon the horse, 

 that the blood coming from the part is red and contains very much more oxygen than 

 ordinary venous blood. 



The observations of MM. Estor and Saint-Pierre show that the blood coming from 

 inflamed parts, in which there is a considerable elevation above the normal temperature, 

 is red, and that it contains from fifty to two hundred and fifty per cent, more oxygen than 

 ordinary venous blood. These facts are regarded as inconsistent with the view that the 

 temperature of parts is due chiefly to oxidation ; but, when we consider the fact that, in 

 the conditions above mentioned, the actual quantity of blood circulating in these parts is 

 increased many times, the error in the deduction is palpable enough. It is not sufficient 

 to show that the blood coming from an inflamed tissue, with an abnormally high temper- 

 ature, contains more oxygen than under ordinary conditions, but it is indispensable to 

 demonstrate that the absolute quantity of oxygen consumed is diminished. For exam- 

 ple, if the venous blood should contain double the normal proportion of oxygen, but the 

 quantity coming from the part should be increased threefold, it is evident that the actual 

 consumption of oxygen would be doubled. As an illustration, let us assume that, in one 

 minute, 100 parts of blood, containing 10 parts of oxygen, circulate through a member, 

 losing in its passage 7*5 parts of oxygen, thus leaving a proportion of 2*5 of oxygen for 

 the venous blood ; if the part become inflamed, let us suppose that, during the same 



