22 ANIMAL MECHANISM. 



into the heart of an animal, in order to ascertain the tempe- 

 rature of the blood which is returning through all the veins 

 of the body into the right cavities, and that of the blood which 

 is coming into the left cavities from the lungs, we find that 

 the blood of the right-hand side of the heart is the warmer ; 

 so that it follows that heat is principally produced along the 

 course of the great circulation. 



If we would more particularly localize the origin of heat, 

 we must take a special organ and investigate, in a com- 

 parative manner, the temperature of the blood which comes 

 to it through the arteries, and goes out of it through the 

 veins. Thus it has been recognized that the muscles, in 

 action, and the glands while they are secreting, are organs 

 for the production of heat ; and in them the most energetic 

 chemical action takes place. 



But we must not expect, when examining all the muscles or 

 all the glands at the moment of their action, to find an un- 

 varying elevation in the temperature of their venous blood. 

 A third element enters into the problem ; it is the loss of 

 heat which takes place while the blood is passing through the 

 organ. Now., all portions of the body are not equally sub- 

 jected to loss of heat ; the most superficial are the most 

 exposed to them, while the deeper organs are sheltered 

 against the causes of cold.* Under these conditions every dis- 

 engagement of heat in the glands ought to be represented by 

 an elevation of temperature in the venous blood. If, on the 

 contrary, we lay the sublingual gland bare, in cold w r eather, 

 and investigate the temperature of the blood in the veins of 

 that gland, we shall find the blood colder than that which 

 lias entered through the arteries. Must we conclude from 

 thence that there has been no disengagement of heat in that 

 gland ? In no wise. We must simply admit that the loss 

 of heat has exceeded its production. 



In short, heat appears to be produced in all the organs, 

 but in various degrees, according to the intensity of the 



* "Wlii-n we wish to ascertain the im n;i e "I 1 t> in] 'nature- of the hlood 

 in the glands, we n.nst rlmosc, fur this investigation, the Mood of the 

 veilis of the livn or the ki<lm\>, mpm.s .slidtrivd IVum OM,lm- inlluuiici-s. 



