CHAPTER V. 
THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 
TuE metabolism of the fasting animal was regarded in the pre< 
ceding chapter as representing the essential demands of the vital 
functions for a supply of matter as a vehicle of potential energy. 
Under these conditions, as we have seen, the total metabolism bears 
a close relation to the mass of active tissue, while the qualitative 
character of the metabolism, that is the ratio of proteid to non- 
proteid matter consumed, appears to be likewise constant for any 
given condition of the body, depending upon the relative supply 
of proteids and non-nitrogenous matters to the active cells. When 
food is given to such an animal the conditions are modified in essen- 
tially three ways: 
First, to the metabolism incident to the fasting state is added 
that required to supply the energy consumed in the reer and 
assimilation of the food. 
Second, the food-supply may alter the proportions i in which the 
various nutrients are supplied to the active cells, and thus affect 
the metabolism qualitatively, giving rise to a relatively greater 
or less metabolism of proteids, fats, carbohydrates, ete. 
Third, the food-supply may be in excess of the requirements of 
the body and lead to a storage of matter of one sort or another. 
The quantitative relations of the food-supply to the total 
metabolism and to the storage of matter and energy in the body 
may be most satisfactorily considered upon the basis of the amounts 
of energy involved. Accordingly we may content ourselves here 
with a simple mention of this side of the question, deferring a dis- 
cussion of it to Part II and confining the present chapter largely 
to a study of the qualitative changes in the metabolism brought 
about by variations in the food-supply. As in the previous chapter, 
it will be convenient to consider the relations of the proteids of the 
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