upon the digestive
tract, whether constipating or laxative in character.

4. Ease of digestion.

5. Effect upon health. It is recognized that there are foods
wholesome and nutritious, that cannot be used by some persons,
while with others the same foods can be consumed with impunity.

As explained in the chapter on Dietary Studies, the nutrients should be
supplied from a number of foods rather than from a few, because it is
believed the various nutrients, particularly the proteins, are not
absolutely identical from all sources, or equal in nutritive value.

EXAMPLES

1. Calculate a ration for a man with little physical exercise.

2. Calculate a ration for a man at hard muscular labor, and give the
approximate cost of the ration.

3. Calculate the amounts of food and the nutrient requirements for a
family of seven for 10 days; five of the family to consume 0.8 as much
as an adult. Calculate the cost of the food; then calculate on the same
basis the probable cost of food for one year, adding 20 per cent for
fluctuation in market price and additional foods not included in the
list.

4. Weigh out the food articles used in problem No. 2, and apportion them
among three meals.

CHAPTER XIX

WATER

263. Importance.--Water is one of the most essential food materials.
It enters into the composition of the body, and without it the nutrients
of foods would be unavailable, and life could not be sustained. Water
unites chemically with various elements to form plant tissue and
supplies hydrogen and oxygen for the production of organic compounds
within the leaves of plants. In the animal economy it is not definitely
known whether or not water furnishes any of the elements of which the
tissues are composed, as the food contains liberal amounts of hydrogen
and oxygen; it is necessary mainly as the vehicle for distributing
nutrients in suspension and solution, and as a medium in which chemical,
physical, and physiological changes essential to life processes take
place. From a sanitary point of view, the condition of the water supply
is of great importance, as impure water seriously affects the health of
the consumer.[87]

264. Impurities in Water.--Waters are impure because of: (1) excessive
amounts of alkaline salts and other mineral compounds; (2) decaying
animal and vegetable matters which act chemically as poisons and
irritants, and which may serve as food for the development of
obje