CHEMICAL PHENOMENA OF RESPIRATION. 319 



Recent analyses of the gases contained in the blood, give, 1 



In 100 parts of arterial blood (in a dog) : 



Oxygen 20 parts, carbonic acid 34.8 parts. 



In 100 parts of venous blood : 



Oxygen 12 parts, carbonic acid 47 parts. 



The brilliant red color of the arterial blood may, perhaps, 

 be caused by a chemical action of the oxygen on the coloring 

 matter, or hematine, but it appears to be chiefly owing to a 

 change of form : under the exciting influence of oxygen, as 

 well as under that of some other agents (chloride of sodium, 

 for instance), the blood globule becomes flatter and slighter, 

 and refracts the light in a different manner from that seen 

 when it is under the influence of carbonic acid ; this latter 

 has the effect of causing it to swell, and approach more nearly 

 the spherical form. 



In passing through the lungs, the blood also, as we have 

 seen, gives off a certain quantity of vapor (the quantity 

 varies, but may be assumed to be at least 300 grins, in 24 

 hours). The exhaled air, indeed, as it leaves the lungs, is 

 nearly saturated with vapor, at a temperature which is 

 nearly that of the body, as has been demonstrated by Gre- 

 hant: we have already seen that if a half-litre of atmo- 

 spheric air be inhaled, the expiration which follows throws 

 off" one-third of this volume of pure air mixed with two-thirds 

 of vitiated air. The vitiated air, which has been for some 

 time in contact with the bronchi, is of the same temperature 

 as the lungs, and is thoroughly moistened ; but the third part 

 of pure air which is immediately given back in breathing, not 

 having remained sufficiently long in the respiratory tree to 

 assume exactly the temperature of its walls, it follows that 

 the entire quantity of air expelled has not the same temper- 

 ature as the body. Grehant has shown, by very close experi- 

 mental researches, that, the temperature of the exterior air 

 being 22 (C.), that of the air exhaled is equal to 35.3 (C.), 

 17 expirations a minute: the exterior temperature being 

 6 (C.), that of the air exhaled is only 29.8 (C.) (Valentin). 

 Grehant has also shown that the air exhaled is surcharged 

 with vapor at its own temperature, and not at that of the 

 body, which is slightly higher (see animal heat). 2 



The blood, therefore, grows cooler as it comes in contact 



1 Ludwig and his pupils. Archiv. de Pfliiger, 1872. 



2 N. Grehant, " Cours de 1'Ecole Pratique." Revue des Cours 

 Scientifiques, Novembre, 1871. 



