34 ZOOLOGY 



(C 6 Hi 2 O 6 ) is broken up, and the oxygen momentarily 

 liberated combines with carbon to form carbon dioxid, 

 while the residue (C 2 H 6 O) is alcohol. In this case 

 the process is simple, direct, and rapid, but ordinarily 

 it is quite otherwise. Various substances may be 

 taken into the body and oxidized without previous 

 change, to a greater or less extent. This is true of 

 alcohol, and this is why it has been claimed that alcohol 

 has a certain food value. The more typical foods, 

 however, are those materials which are broken up or 

 reduced and then built up into the living substance 

 itself. This is the anabolic process, and the opposite 

 or katabolic process is that in which this living material 

 is oxidized with the production of work in the sense 

 already denned. Thus we finally see that respiration 

 has to do with the life activities of every cell, and the 

 conception of it as taking place merely in the lungs is 

 quite erroneous. Breathing is seen to be merely a means 

 directed toward a respiratory process which is going 

 on all over the body. 



Blood a 8. There is plenty of evidence showing that the 



oxygen oxygen absorbed by the lungs is not all used up in 

 those organs. The red corpuscles (red only in mass) 

 in the blood contain a substance called hemoglobin, 

 which readily takes up oxygen, but also readily gives 

 it up. The corpuscles, circulating with the blood, 

 carry the oxygen to every part of the body. Much, 

 though by no means all, of this oxygen is set free in 

 the smallest vessels, and the blood returning to the 

 heart in the veins contains less oxygen and correspond- 

 ingly more carbon dioxid, the product of combustion. 

 The difference in color of the blood is connected with 

 these changes ; the arterial blood, rich in oxygen, is 

 bright red ; the venous blood, dark purple. 



