INTRODUCTION. XIX 



would prevent the sensible heat of the blood in 

 the lungs being greater than that of the rest of 

 the system, as the quantity generated by the 

 chemical changes is immediately lost in the 

 greater capacity of the arterial fluid. A few 

 years ago, Dr JOHN DAVY investigated the ca- 

 pacity of the arterial and venous blood, and his 

 experiments are by no means favourable to the 

 conclusions of CRAWFORD. The difference of 

 capacity between the arterial and venous fluids 

 was observed to be so much less than what is 

 stated by the latter gentleman, that the conser- 

 vation of uniform temperature is scarcely to be 

 explained by it. Indeed, the arterial blood is al- 

 lowed by MENZIES, PL.ENK, DAVY, MAGENDIE, 

 THENARD, and many others, to be at least one 

 degree warmer than the venous. If this be 

 correct, it militates considerably against the 

 doctrine of CRAWFORD. Since the completion 

 of this work, an idea has struck me, which 

 appears sufficient, in conjunction with prin- 

 ciples already stated, to explain satisfactorily 

 the source of animal heat. It does not militate 

 against the principles which have been deve- 

 loped in the present Experimental Inquiry. 



