^ECT. II.] Physiologjj. 297 



carbon and hydrogen for tlie blood. In proportion 

 as the oxygen unites with tlie hydrogen and car- 

 bon, water and carbonic acid are formed; the ca- 

 loric combines with the venous blood, which, in 

 losing its carbon and hydrogen, becomi^s arterial, 

 and has its capacity for containing caloric immedi- 

 ately augmented. The blood, now become arterial, 

 in its circulation through the body, gradually ab- 

 sorbs carbon and hydrogen, repasses to the venous 

 state, and sets ivQQ a portion of caloric in ])ro- 

 portion as its capacity for containing it is dimi- 

 nished. According to this doctrine, therefore, the 

 almost uniform temperature in all parts of the body 

 is owing to the gradual and successive changes of 

 arterial blood to venous throughout the body, and 

 of venous to arterial in the lungs. It is also agree- 

 able to this doctrine to suppose that the higher 

 temperature of some parts of the body may be 

 caused by arterial blood absorbing more carbon 

 and hydrogen, or, in other words, becoming more 

 rapidly venous. 



However ingenious this explanation deserves to 

 be regarded, it has not been deemed satisfactory. 

 The difference in specific caloric, admitting the 

 calculation to be accurate, is justly thought too 

 small to account for the great quantity of heat 

 which must be evolved. And if the opinion of 

 some be true, that the carbonic acid gas and water 

 emitted in expiration are not formed in the lungs, 

 but during the circulation, this doctrine nuist be 

 altogether untenable. 



This defect in Dr. Crawford's hypothesis might 

 perhaps be remedied, if Mr. Davy's supposition 

 of air enterimr the blood and combining with it in 



