CHAPTER X 



INTERMEDIATE METABOLISM 



We shall now take each class of foodstufE in turn, and 

 after summarising the changes which it undergoes during 

 digestion, follow the transformation which it undergoes 

 between absorption and excretion. Such transformation 

 will be found to involve any of the following — 



1. Conversion of molecules not immediately required 

 for consumption into storage forms. 



2. Incorporation into the structure of the living cell. 



3. Conversion of one form of foodstuH: into another, as, 



for instance, proteins into carbohydrates. 



4. Conversion of toxic into non-toxic bodies. 



5. Breakdown changes preparatory to oxidation. 



6. Oxidation itself. 



1.— METHODS OF INVESTIGATION 



Among the methods employed for investigating these 

 intermediate reactions are the following : — 



1. The direct estimation of substances in the blood, 

 tissues and excretions. 



2. Administration of Intermediate Substances. — A sub- 

 stance, A, given to the body is excreted in the form D. 

 There are two substances, B and C, which might from a 

 chemical point of view be intermediate stages in the change. 

 B and C are injected into the animal. If B is excreted 

 unchanged, and C is converted ijito D, the inference is 

 drawn that the normal course of metabohsm is A -> C -> D 

 rather than A -> B -> D. 



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