Chap. 32;] Animal Heat. .339 



place in the combination of heat with ice conftituting 

 water. This latter difference is called a difference in ca- 

 pacity for heat, by which is unclerftood an inequality in 

 the quantity of abfolute heat in two bodies, though their 

 temperatures and weights are equal. Thus, if a pound 

 of water and a pound of diaphoretic antimony have a 

 common temperature, the quantity of abfolute heac 

 contained in the former is nearly four times that con- 

 tained in the latter. 



The following is a brief ftatement of Dr. Craw- 

 ford's ingenious theory of animal heat. He made a 

 feries of experiments, by which he found, that the fixed 

 air and aqueous vapour, which are difcharged from 

 the lungs, contain only about one-third part of the ab- 

 folute heat contained in the atmofpherical air, previ- 

 ous to its being refpired: air, therefore, in becoming 

 fubfervient to refpiration, lofes part of its heat. He 

 has alfo fhewn that the abfolute heat of florid ar- 

 terial blood is to that of venous nearly as eleverr and 

 an half to ten -, fince,' therefore, the blood, which is re- 

 turned by the pulmonary veins to the heart, has its 

 quantity of abfolute .heat increafed, he fairly concludes 

 that it muft have acquired this additional heat in the 

 lungs. From the preceding obfervations it appears, 

 that the production of animal heat depends on a pro- 

 cefs analogous to chemical elective attraction, and 

 which is* regulated by the following principles. Vital 

 air contains more abfolute heat, in proportion to its 

 temperature and weight, than fixed air. The blood is 

 returned to the lungs impregnated with the carbona- 

 ceous principle ; the blood has lefs attraction for that 

 principle than vital air has ; in the lungs, therefore, 

 it quits the blood to unite with the vital air. By this 

 combination the vital air is changed into fixed air, and 

 depofits part of its heat : the capacity of blood for heac 

 Z2 is 



