168 STORRS AGRICULTURAL EXPERIMENT STATION. 
which a given amount.and kind of food will furnish to the 
body is called its fuel value, and is expressed by calories, one 
calorie representing the energy necessary to lift 1 ton.1.54 feet 
or to raise the temperature of 1 pound of water 4°F. The 
fuel value of fats is more than twice as great as that of protein 
or carbohydrates, and hence materials rich in fat have a rela- 
tively high fuel value. 
Of course the body is not nourished by what is actually eaten, — 
but what is actually digested, that is by that part of all the 
food eaten which the digestive organs are able to change into 
such form that it can be taken into the circulation and used to 
build tissues or supply heat and energy. The amount thus 
made useful we speak of as the digestible portion. It differs 
somewhat with individuals, with the mode of cooking, etc., but 
in general it is found that about 97 per cent. of the total pro- 
tein in meats and 95 per cent. of the total fat 1s digested by the 
average healthy person, or, in other words the digestibility of 
animal protein is 97 per cent., and of fats 95 per cent. 
In considering the true nutritive value of any food, then, we 
must know in the first place how much refuse and water it 
contains. ‘The more of these we find present, the smaller will 
be the proportion of nutrients; and the greater the proportion 
of fats and carbohydrates, the higher will be the fuel value. 
In discussing the value of poultry as food it may be interest- 
ing to notice how the different kinds of meats, taken as a class, 
compare in nutritive value with the other classes of foods, such 
as milk, eggs, vegetables, fruits, cereals, bread, etc. The com- 
position of different meats and other foods is given at the 
bottom of Table 27. It is rather hard to make very general 
comparisons as the different vegetable foods vary so greatly in 
their composition; but it is safe to say that meats, as a rule, 
have a smaller amount of indigestible nutrients, more protein 
and fat, and practically no carbohydrates. ‘This means that 
they are more completely digested and furnish more of the 
material needed for tissue-building in the body. ‘They also 
supply a good amount of fat, but not in such large proportions 
that unless large amounts of fat meat such as pork or bacon 
were eaten the body could get all the fuel it needed from them 
without getting a superfluous amount of protein. A diet of 





