236 ANIMAL HEAT. 



The temperature of solids is more easily affected by a given 

 quantity of caloric, than that of fluids, and the temperature of 

 fluids than that of aeriform bodies; or, in other words, solids have 

 a smaller capacity for caloric than fluids; and fluids than aeriform 

 bodies. If, therefore, a solid becomes fluid, or a fluid aeriform, it 

 absorbs a great quantity of caloric, notwithstanding its temperature 

 remain precisely the same. And the converse holds equally good : 

 if an aeriform substance becomes liquid, or a liquid solid, the 

 caloric which it before contained is now, from its diminished capa- 

 city, much more than sufficient for the temperature which before 

 existed, and the temperature of the body accordingly rises. 



In respiration, the dark blood of the pulmonary artery parts 

 with a portion of its carbon, and acquires a florid hue. Oxygen 

 disappears, and carbonic acid is expired with the other consti- 

 tuent of the atmosphere nitrogen or azote, which seems 

 usually to have experienced little or no change from inspiration. 



The celebrated Dr. Crawford of St. Thomas's Hospital appeared 

 to prove, by his experiments, that the arterial blood has a larger 

 capacity for caloric than the venous, and common air than car- 

 bonic acid gas. He therefore argued thus : when the carbonic 

 acid appears in the lungs, the smaller capacity of this than of 

 common air for caloric, must cause an increase of temperature ; 

 but the blood, having changed from venous to arterial, has 

 acquired a greater capacity than before, and absorbs the heat 

 given out by the carbonic acid. The blood, of course, does not 

 become warmer, because the caloric is not more than sufficient 

 to render its temperature equal to what it was previously ; and, 

 indeed, according to some, it is not quite sufficient for this, since 

 the temperature of the florid blood of the pulmonary veins has 

 appeared two degrees lower than that of the pulmonary artery to 

 some experimenters, although the greater number have found 

 it a degree or two higher than the dark blood. 



The body in this way acquires a fund of caloric, and yet the 

 lungs, in which it is acquired, do not experience any elevation of 

 temperature ; or, if they do, this is very inconsiderable. 



The arterial blood, charged with much caloric, which, as it 

 circulates through the small vessels, is not sensible, becomes 

 venous, acquires a dark hue, and its capacity for caloric is 

 diminished ; consequently its temperature rises, the caloric 

 which was previously latent is, from the decrease of capacity, 

 sufficient to raise its temperature, and is evolved. In this mode, 



