FOOD DIGESTION AND RESPIRATION 



73 



Many of these are of importance, because they play a part in 

 various chemical reactions in the cell, and in the abnormal changes 

 of disease. Lactic acid is one of the most important intermediate 



O 



-s 



FlG. I. Diagram of the Carbohydrate Cycle from Carbon Dioxide through 

 Starch to Carbon Dioxide again. 



products of carbohydrates on account of its relation to muscle, 

 as will be seen later. 



In Fig. i a diagram is given of the carbohydrate cycle. 



Fat 



We have already learned something of the chemical nature of 

 fats as esters of glycerol and, incidentally, the fact that there is an 



