262 A. I. RINGER AND EMIL J. 



carbohydrates are converted into glucose. We can therefore see that glu- 

 cose is the main channel of chemical action in the animal body, for from 

 all sides the reaction swings in its direction. 



But the cells of the body cannot oxidize glucose directly. The glucose 

 molecule must first undergo a series of reactions during which it is broken 

 up into much smaller and simpler compounds, and' only those can be oxi- 

 dized by the cells to yield energy. We may liken the process to the grind- 

 ing down of grain to a flour in a mill, which is at the same time forcing 

 the product through a series of sieves, each consecutive sieve having smaller 

 and smaller meshes. Only those particles that can go through the finest 

 mesh will be fit for consumption. All the others must be reground. One 

 difference between the mill and the animal body is that in the mill the 

 process is irreversible, that is to say, a particle that is once ground down 

 remains so, whereas in the animal body the process is a reversible one, 

 the particles possessing the power of again polymerizing and flying back 

 into an upper sieve. The result is a continuous and endless grinding pres- 

 sure from above and a continuous flying back to the upper sieves. 



The grinding down process may be illustrated thus (the double arrow 

 showing where the process is reversible). 



GLUCOSE 



Glyceric Aldehyde v N Glycerol * To fat formation. 



Jf 



Pvruvic Aldehyde 



.Jf.\\ 



Lactic Acid ^ZTll Alanin^nl To protein formation. 

 Pyruvic Acid 



J 



Acetaldehyde Aldol Condensation > Fatty acid formation 



Acetic Acid Alcohol 



II 



/\ 



CO 2 H 2 O CO 2 H 2 O 



The study of the intermediary metabolism of carbohydrates is fraught 

 with great difficulty. In the first place we deal with substances that are 



