548 IMPORTANT RESEARCHES 



These experiments show that there is more 

 oxygen and nitrogen in arterial than venous 

 blood, and a little more carbonic acid in the 

 latter. But if they prove anything in regard to 

 the theory of respiration, it is, that carbonic acid 

 is not formed in the general circulation. For if 

 generated in the arterial blood, it ought to contain 

 more carbon than venous blood, which is not the 

 case ; and if in venous blood, its temperature ought 

 to be higher than that of the arteries ; for the 

 obvious reason, that caloric is always evolved 

 during the formation of carbonic acid. But the 

 most decisive proof that the latter is generated in 

 the lungs, and not in the general circulation, is, 

 that the temperature of arterial is higher than 

 that of venous bloody as long ago observed by 

 Haller, Black, Plenck, and Menzies. 



This important fact, which was denied by 

 Cullen, and overlooked by nearly all other phy- 

 siologists, has been completely established by 

 the experiments of Dr. John Davy, Magendie, 

 and Holland. In an excellent paper, recorded 

 in the Philosophical Transactions for 1814, it 

 was shown by Davy, that in lambs, sheep, and 

 oxen, the blood is from 1 to 1.5 warmer in the 

 carotid arteries and left ventricle of the heart 

 than in the jugular veins and right ventricle. 



In another series of observations made in 1838, 

 and recently published among other physio- 

 logical researches, he has shown, that in sheep, 



