CHEMICAL COMPOSITION OF FOOD-FISHES. 821 
The edible substance consists of (1) water, (2) nutritive substance 
or nutrients. 
The water, refuse, and the salt of salted meat and fish are called non- 
nutrients. The water contained in foods and beverages has the same 
composition and properties as other water ; it is, of course, indispensa- 
ble for nourishment, but it is not a nutrient in the sense in which it is 
here used. In comparing the values of different food materials for 
nourishment, the refuse and water are left out of account. 
PRINCIPAL NUTRIENTS OF FOOD. 
Protein : 
Albuminoids: e. g., albumen of egg, myosin of 
muscle (lean of meat), casein of milk, gluten 
of wheat. 
Gelatinoids : e. g., ossein of bone, collagen of ten- 
dons (which yielded gelatin). 
Fats : e. g., fats of meat, butter, olive oil, oil of maize 
and wheat. 
Carbohydrates : e. g., starch, sugar, cellulose (woody 
fiber). 
Mineral matters or ash: e. g., calcium, potassium, and 
sodium, phosphates and chlorides. 
WAYS IN WHICH THE NUTRIENTS ARE USED IN THE BODY. 
The protein of food 
forms the (nitrogenous) basis of blood, muscle, con- 
nective tissue, etc., 
is transformed into fats and carbohydrates, 
is consumed for fuel. 
The fats of food 
are stored as fat, 
are consumed for fuel. 
The carbohydrates of food 
are transformed into fat, 
are consumed for fuel. 
POTENTIAL ENERGY OF FOOD. 
In being consumed for fuel, the nutrients yield euergy in the forms of 
heat, which keeps the body warm, and muscular energy, strength for 
work. The quantities of energy which different food materials are 
capable of yielding are determined by experiments with the respirative 
apparatus and the calorimeter. In their use as fuel in the body the 
nutrients appear to replace one another in proportion to their potential 
energy as indicated by their heats of combustion. This energy, which 
is accordingly taken as the measure of their fuel value, is estimated in 
