

nt hate lh wt ee 

POULTRY AS FOOD. 167 
The figures given in Table 23 show the percentages of the 
different ingredients as found by analysis. In Table 27 above 
the values have been computed so as to show the proportions 
of digestible nutrients in poultry; and for the sake of com pari- 
son and discussion of relative values, corresponding figures are 
given for a number of common food materials other than poultry. 
In order to get at the real meaning of these figures, a few of 
the main principles of food and its uses in the human body 
must be borne in mind. Food is taken into the body to build 
new tissues, fluids, etc., repair old or injured ones, and to fur- 
nish heat to keep the body warm and energy for all muscular 
work, for blood circulation and for breathing as well as for 
walking or any other activity. 
Not all the material in food as it is bought, or even in food 
ready to eat, is useful to the body. Most foods as purchased 
contain more or less refuse, or parts which are quite useless as 
nourishment. ‘The skin and seeds of vegetables, the shells of 
eggs and the bones of fish and meat are examples of refuse. 
Moreover there is more or less water in all food materials, and 
though water is necessary to the well-being of the body, that 
contained in ordinary solid foods is not counted as adding to 
the real nutritive value of the food. 
Coming to the actual nutrients of the food we find that the 
materials which are needed to build up the body are the nitrog- 
enous substances called protein and small quantities of mineral 
matters. The heat and energy are ordinarily supplied mainly 
by fats and by carbohydrates, of which latter starches and 
sugars are the main representatives in our food, although pro- 
tein may also be thus utilized. The protein is found in casein 
of milk, white of egg, gluten of wheat, etc., and also in the 
lean of meat. Fats are of course easily recognizable in meats 
and butter, and occur more or less in vegetable foods, as the 
oil of corn or wheat, olive oil, etc. The principal sources of 
carbohydrates are the starches of cereals; vegetables and fruits, 
and sugars, whether separated or in honey and vegetable foods. 
Mineral matters are found in small quantities in all our com- 
mon foods. Meats are especially important in our diet as 
sources of the tissue-building protein, but they also have a 
great value for the heat and energy they yield to the body, 
especially through the fat. The amount of energy or heat 
