t be included in its upkeep. The replacing of the dead and cast out
cells with new ones, the repairing of the worn cells, the furnishing
of heat, not only for the running of the engine but for the
maintenance of the body temperature,--all of these must be considered
and cared for if life is to continue. In man-made machinery, the
renewal of the worn parts, and the replacing of those no longer useful
must be accomplished by an outside agency. But in the body this work
is performed by the organism; and the material used for the purpose,
as well as that which is used to furnish the heat necessary for the
internal and external activities of the body is food.

~Exceptions to this Rule.~--Under normal conditions the body never
uses its own structure either for fuel or to replace tissue losses. In
starvation the body rebuilds its important tissues, such as the nerves
and glands, at the expense of the less important ones, such as the
connective tissues and the skeletal muscles (Taylor).

Science has proved that for the most part the body does not use the
food materials in their original form, but carries them through a
series of transformations into substances more easily handled by the
organism.

Roughly speaking, we may say that the body carries the foodstuffs
through practically four processes on the pathway through the body,
namely, digestion, absorption, metabolism, elimination.

~Processes Included in Digestion.~--There are several processes
concerned in this transformation of the food materials. Some are
purely mechanical and have to do with the movement of the food mass
through the digestive tract: others are of a chemical character and
bring about distinct changes in the food materials themselves. These
mechanical and chemical processes with the retarding and stimulating
agents that influence them are called digestion.

~Absorption.~--After the food materials have undergone digestion, or
simplification into more available substances, these substances are
absorbed, that is, they are passed through the membranes lining the
walls of the intestinal tract, and thence to the blood.

~Metabolism.~--The utilization of the transformed food materials and
their final fate in the human body is included under the term
Metabolism.

~Elimination.~--After the food materials have been utilized to the
extent of the body's ability to handle them, their waste products are
cast out of the organism by way of the skin, the lungs, the