RESPIRATION. GlQ 



respiration, others affirm that a portion of it is absorbed as well 

 as of the oxygen. While a third party, and that by far the most 

 numerous, conceive that a portion of azotic gas is emitted from 

 the blood in the lungs ; that this portion just balances the por- 

 tion of oxygen which has combined with hydrogen, and thus pre- 

 vents any diminution in the bulk of the air from becoming sen- 

 sible. 



If we adopt the view of Dr Priestley and Professor Liebig, 

 that a great deal of air is carried to the stomach by the saliva, 

 and that this air makes its way into the blood, and that its azo- 

 tic portion is emitted in the lungs in a gaseous form, we see a 

 source for the origin of the azotic gas that may be evolved in 

 the lungs. 



It is obvious that the 108 cubic inches of air remaining in the 

 lungs after a full expiration, must contain less than the normal 

 quantity of oxygen. Hence, even admitting that the azote of 

 the air is not affected by respiration, still the air expired would 

 appear to contain an excess of azote, or a greater bulk than ex- 

 ists in common air. I think it not unlikely that this may be the 

 reason of the apparent increase of azotic gas in the air expired. 



8. It is most probable that the blood, as it passes through the 

 lungs, absorbs oxygen from the air inspired ; and that, during 

 the circulation of the blood through the capillary vessels, this 

 oxygen is converted partly into carbonic acid and partly into wa- 

 ter. Tiedemann and Gmelin suppose that this carbonic acid com- 

 bines with the soda of the blood, and is displaced during the cir- 

 culation by lactic acid, while the lactate of soda is decomposed in 

 its turn by urea. This hypothesis, or something very like it, has 

 been embraced by Dumas. But Liebig's explanation given above 

 is more plausible. We do not know enough respecting the nor- 

 mal state of the constituents of blood, consisting chiefly of albu- 

 men and cruorin, to be able to point out the change effected by 

 this abstraction of carbon and hydrogen.* But there is reason 



* MM. Macaire and Marcet analyzed dried arterial and venous blood, and 

 oundthat venous blood contained more carbon and less oxygen than arterial blood. 



Dried arterial blood. Dried venous. 

 Carbon, . 50-2 55-7 



Azote, . 163 16-2 



Hydrogen, . 6-6 6*4 



Oxygen, . 26 -3 21-7 



99-4 100-0 



See Mem. de la Societe de Phys. ct d'Hist. Nat. de Geneve, v. 223. 



