ame individual in all conditions; as vocation,
health, exposure, habits of life, season, climate, &c., influence the
condition of the system.

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What does observation show? 288. What is said of the causes of
hunger? 289. Why is not the same kind of food adapted to different
individuals?

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290. All articles of food may be considered in two relations: 1st, As
nutritive. 2d, As digestible. Substances are nutritious in proportion
to their capacity to yield the elements of chyle, of which carbon,
oxygen, hydrogen, and nitrogen are the most essential; they are
digestible in proportion to the facility with which they are acted
upon by the gastric juice. These properties should not be confounded
in the various articles used for food.

291. As a "living body has no power of forming elements, or of
converting one elementary substance into another, it therefore follows
that the elements of which the body of an animal is composed must be
in the food." (Chap. III.) Of the essential constituents of the human
body, carbon, hydrogen, oxygen, and nitrogen are the most important,
because they compose the principal part of the animal body; while the
other elements are found in very small proportions, and many of them
only in a few organs of the system. (Appendix G.)

_Observation._ Nitrogen renders food more stimulating, particularly if
combined with a large quantity of carbon, as beef. Those articles that
contain the greatest amount of the constituent elements of the system
are most nutritious. As milk and eggs contain all the essential
elements of the human system, so they are adapted to almost universal
use, and are highly nutritious.

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290. In what proportion are substances nutritious? Digestible? Why
does beef stimulate the system? What is said of milk and eggs?

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292. The following table, by Pereira, in his treatise on Food and
Diet may aid the student in approximating to correct conclusions of
the quantity of nutriment in different kinds of food, and its
adaptation to the wants of the system.

TABLE,

SHOWING THE AVERAGE QUANTITY OF DRY, OR SOLID MATTER, CARBON,
NITROGEN, AND MOISTURE, IN DIFFERENT ARTICLES OF DIET.

-------------------+---------+---------+-----------+------------
One hundred Parts. | Dry | Carbon. | Nitrogen. | Water
| Matter. | | |
-------------