3OO 
bines with the blood; and from whatever cause, 
therefore, the red colour of the blood may proceed, 
we may safely conclude, that it cannot arise from 
the combination of oxygen. It forms no part of 
our present intention to inquire farther into the cause 
of this redness of the blood ; it is sufficient, for our 
present purpose, to have shewn that it cannot pro- 
ceed from its oxygenation. 
596. IN our former work, we maintained (129.), 
not only that no oxygen entered the blood, but that 
the same circumstance might be affirmed of the ni- 
trogenous portion of the air. This we stated to have 
been uniformly the opinion of M. Lavoisier, who, we 
are told, ascertained, by rigorous experiments, that 
neither an increase nor diminution of nitrogen occur- 
red in respiration *. Such too was the conclusion of 
Goodwyn and Menzies ; and it is borne out by the 
results afforded in the respiration of all the lower 
animals. In his late experiments, Dr Thomson ob- 
served a deficiency in the quantity of nitrogen ; but it 
was very inconstant, and sometimes scarcely percep- 
tible ; and he therefore deems it rather an acciden- 
tal, than necessary, condition of respiration ! In 
the experiments of Messrs Allen and Pepys on the 
respiration of a Guinea pig (568.), no change what- 
ever occurred, either in the quantity, or the quality of 
* Mem cle 1'Acad. an. 1789) p. 574. 
Syst. Cbem, vol. v. p. 737, 3d edit. 
