208 



APPLIED PHYSIOLOGY 



comes of a brighter red color as it gains oxygen, Car- 

 bonic acid, which was combined with the alkalies of the 

 blood plasma, passes through the capillary wall into the 

 air of the air sac as easily as the oxygen entered the blood. 



355. The skin and stomach as respiratory organs. 

 Wherever the blood tubes are in contact with the air, 

 absorption of oxygen will take place. In the stomach and 

 intestine the blood tubes are very near the surface, and 

 are in contact with air swallowed with the food. So some 

 oxygen will be absorbed and some oarbonic acid gas given 

 off. The skin also absorbs oxygen and gives off carbonic 

 acid gas. In a frog at least J of the respiration is per- 

 formed in this Way. In man, about ^^ as much respira- 

 tion is carried on by the skin, stomach, and intestine as by 

 the lungs. 



356. Respiration of the cells of the body. After leaving 

 the lungs, the blood is distributed through the arteries, 



and enters the capillaries 

 of the body. As it enters 

 the capillaries it contains 

 the same amount of gases 

 as when it left the lungs ; 

 that is, each 100 cubic 

 inches of blood contains 

 40 cubic inches of car- 

 bonic acid gas and 20 of 

 oxygen. As it leaves the 

 capillaries, it contains the same amount of the gases as 

 the venous blood which enters the lungs; that is, each 100 

 cubic inches contains 46 cubic inches of carbonic acid gas 

 and 12 of oxygen. The exchange in the capillaries bal- 

 ances the exchange in the lungs. 



When a piece of flesh is put into a dish of blood, oxygen 



Diagram of the respiration of cells. 



