PART I. 
THE INCOME AND EXPENDITURE OF MATTER. 
CHAPTER I. 
THE FOOD. 
THE supply of matter to the body is, of course, contained in the 
food, including water and the oxygen taken up from the air. In 
a more limited and familiar sense, the term food is employed to 
signify the supply of solid matter, or dry matter, to the animal. 
It is proposed here simply to recall certain familiar facts relative 
to the composition and digestibility of the food in this narrower 
sense, taking up the subject in the barest outline. 
Composition.—While a vast number of individual chemical 
compounds are found in common feeding-stuffs, the conventional 
scheme for their analysis unites these substances into groups and 
regards feeding-stuffs as composed, aside from water and mineral 
matter, essentially of protein, carbohydrates and related bodies, 
and fats. Or, setting aside the mineral ingredients, the “organic” 
ingredients may be divided into the nitrogenous, comprised under 
the term protein, and the non-nitrogenous, including the fats and 
carbohydrates. 
Protein.—The name “protein” originated with Mulder, who 
used it to designate what he supposed to be a common ingredient 
of all the various proteids, but it has since come to be employed as a 
group name for the nitrogenous ingredients both of feeding-stuffs 
and of the animal body. 
The amount of protein in feeding-stuffs we have at present no 
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