me protein material is also found in the vegetable
world. This class of foods contains carbon, oxygen, and hydrogen, and
in addition, two substances not found in carbohydrates or
fats--namely, sulphur and nitrogen. Proteids always contain nitrogen,
and hence they are frequently spoken of as nitrogenous foods. Since
the proteids contain all the elements found in the two other classes
of foods, they are able to contribute, if necessary, to the store of
bodily energy; but their main function is upbuilding, and the diet
should be chosen so that the proteids do not have a double task.

For an average man four ounces of dry proteid matter daily will
suffice to keep the body cells in normal condition.

It has been estimated that 300,000,000 blood cells alone need daily
repair or renewal. When we consider that the blood is but one part of
the body, and that all organs and fluids have corresponding
requirements, we realize how vast is the work to be done by the food
which we eat.

64. Mistakes in Buying. The body demands a daily ration of the three
classes of food stuffs, but it is for us to determine from what
meats, vegetables, fruits, cereals, etc., this supply shall be
obtained (Figs. 28 and 29).

[Illustration: FIG. 28.--Table of food values.]

[Illustration: FIG. 29.--Diagram showing the difference in the cost of
three foods which give about the same amount of nutrition each.]

Generally speaking, meats are the most expensive foods we can
purchase, and hence should be bought seldom and in small quantities.
Their place can be taken by beans, peas, potatoes, etc., and at less
than a quarter of the cost. The average American family eats meat
three times a day, while the average family of the more conservative
and older countries rarely eats meat more than once a day. The
following tables indicate the financial loss arising from an unwise
selection of foods:--

FOOD CONSUMED--ONE WEEK
|===========================|=======================================|
| FAMILY No. 1 | || FAMILY No. 2 |
|---------------------------|---------------------------------------|
|20 loaves of bread | $1.00 ||15 lb. flour, bread |
|10 to 12 lb. loin steak | || home made (skim milk used) | $.45
| or meat of similar cost | 2.00 ||Yeast, shortening, and |
|20 to 25 lb. rib roast | || skim milk | .10
| or similar meat