340 J>. Crawford's Theory. [Book IX. 



is at the fame time increafed ; the blood therefore rc- 

 teives that portion of heat which was detached from 

 the air. 



The arterial blood,- in its pafTage through the" ca- 

 pillary veffels, is again impregnated with the carbo- 

 naceous principle, and the bafis of inflammable air, by 

 which its capacity for heat declines ; it, therefore, 

 in the courfe of the circulation, gradually grves out 

 the heat which it had received in the lungs, and diffufes 

 it over the whole body. Thus it appears, that in its 

 circulation through the lungs the blood is contimfally 

 difcharging carbonaceous matter and abforbing heat, 

 and that in its pafiage through the other parts of the 

 body it is perpetually imbibing carbon and emitting 

 heat. In this account of animal heat I have entirely 

 omitted the abforption of vital air. This abforption was 

 not admitted by Dr. Crawford, and, though eftablifhed 

 by the experiments of Dr. Prieftley, does not? at all 

 invalidate the theory of the former philofopher. It is 

 confident with either hypothefis, that the blood in the 

 lungs gains the heat which is loft by the air ; and upon 

 the truth of this propofition refts the theory of Dr* 

 Crawford. 



By the different capacity which blood poffefles for 

 heat in its different ftates,"it is capable of fupplying the 

 different parts of the body with heat, while its own 

 temperature remains the fame. If this difference of 

 capacity for heat did not exift, the extremities of the 

 body cpuld not be properly fupplied with heat from the 

 lungs, unlefs the lungs themfelves were expofed to a 

 degree of heat which would be certainly prejudicial,. 

 and, perhaps, fuch as no organiied fubftance could fup- 

 port without deftru&ion. 



Dr. Crawford has moreover proved, by a courfe of 



experiments, that when an animal is placed in a cold 



* medium, 



