208 MAX KLEIBER 



books on nutrition, therefore, energy relationships are dealt with as a 

 subject of mere historic interest. In these extreme cases, as DuBois 

 puts it, nutrition becomes synonymous with dietetics. When the 

 period of predominant expansion is superseded by a period of intensi- 

 fication of knowledge in nutrition, interest in energy relations will 

 probably be renewed. Such a tendency is already noticeable since 

 vitamins and their functions are linked to enzymes, and the impor- 

 tance of a considerable part of these enzymes is best understood as that 

 of catalysts required in the metabolic processes that provide the en- 

 ergy necessary in all manifestations of life. 



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