^88 RESPIRATION. 



vessels is dependent upon external physical effects, we might 

 rather wonder at the slight diminution of the temperature in 

 arterial blood, and apply this observation in support of the as- 

 sumption of a chemical absorption of oxygen. 



Although we can scarcely any longer entertain the slightest 

 doubt that a large portion of the absorbed oxygen enters into 

 chemical combinations in the arterial blood, we are not on that 

 account justified in assuming that carbonic acid and water are 

 already formed within the arterial blood, for this is an assumption 

 which has already led to many erroneous theories regarding the 

 respiration. As the serum is only capable of absorbing a small 

 quantity of oxygen, and as we find that the blood-corpuscles 

 change so essentially in the capillaries, the more probable view 

 will always be, that the oxygen is conveyed from the blood- 

 corpuscles to the capillaries in a loosely combined state, and that 

 it passes from thence into the parenchymatous fluids in order 

 there to commence effecting oxidations, among the products of 

 which we find carbonic acid and water. We have already en- 

 deavoured to show that wherever oxygen and organic matters 

 enter into combination, they do not at once yield carbonic acid 

 and water as the products of their combustion, and that these 

 simple oxides (as in putrefaction and decomposition) are often 

 only simply separated from the oxidised body, without the organic 

 body being entirely destroyed, as in combustion. We must, how- 

 ever, beware of adopting such an exclusive view as to maintain 

 that there is no generation of carbonic acid or even of water within 

 the lungs, or between the left side of the heart and the capillaries, 

 after the oxygen has been absorbed in the blood. We might more 

 readily adduce proofs of the formation of a part of the carbonic 

 acid after the first contact of the blood with the atmosphere, than 

 the contrary. Magnus has certainly found relatively less, but 

 absolutely more, carbonic acid in venous than in arterial blood ; 

 and although we may not regard this individual observation as one 

 of constant occurrence, we can scarcely interpret it in any other 

 way than that, at least in this case, carbonic acid is developed after 

 the access of oxygen to the venous blood. In fact, we must 

 obstinately adhere to a pre-conceived opinion, if, notwithstanding 

 the important differences recently made known to us in the 

 arterial and venous blood, we should still maintain that the blood 

 remains wholly unaffected by the oxygen with which it is charged 

 in the lungs, and that any one of its constituents cannot intimately 

 appropriate to itself the oxygen without losing it again in the 



