RESPIRATION OF THE TISSUES 2CK) 



will leave the red blood cells and combine with the cells 

 of the flesh. In a similar way oxygen leaves the red blood 

 cells in the capillaries and, passing through their thin walls, 

 unites with the cells of the body, producing carbonic acid 

 gas, water, and urea. The water and urea go back to the 

 blood and are thrown off by the kidneys. The carbonic 

 acid gas passes through the capillary wall into the blood 

 and unites with the alkalies of the plasma. This goes on in 

 every capillary and cell of the body and constitutes the 

 real act of respiration. The lungs and red blood cells are 

 only devices for carrying oxygen to the deep cells of the 

 body. 



357. Oxidation of SUgar and fat. Neither sugar nor fat 

 becomes a living part of the cells of the body, but after being absorbed 

 both are oxidized at once and furnish about three times as much heat 

 and energy as the albumin, which forms a part of the cells. But oxi- 

 dation in the body is a living process, and requires the operation of 

 living tissues. So it is unlikely that it occurs in the blood stream. As 

 sugar is absorbed, the cells of the liver take it into their own substance,, 

 and probably oxidize it there. In the same way the fat is probably 

 taken up by the epithelial cells of the air sacs of the lungs and oxidized. 

 In each case the heat is distributed through the whole body by the 

 blood. 



358. Respiration a continuous process. When the 

 breath is held, the oxygen in the lungs and that carried 

 by the red blood cells is sufficient to supply the body for 

 only about half a minute. By the end of that time all the 

 blood becomes venous and a great shortness of breath is 

 felt. 



Oxygen passes from the lungs through the blood tubes 

 to the cells of the body with great rapidity, so that by a 

 few deeper breaths enough extra oxygen is taken up by 

 the red blood cells to relieve shortness of breath caused 

 by their lack of oxygen. 



OV. PHYSIOL. 14 



