is kinetic transformed into potential energy and _vice
versa_, but the different forms of kinetic energy (heat, light,
electricity, sound, and mechanical motion) are readily transformed
the one into the other. With suitable devices, mechanical motion can
be changed into heat, sound, or electricity; heat into motion and
light; and electricity into all the other forms of energy. These
transformations are readily explained by the fact that the different
varieties of kinetic energy are but different forms of motion (Fig.
84).

73 The simplest arrangement of the parts of a gland is that where they
are spread over a plain surface. This arrangement is found in serous
membranes, such as the pleura and peritoneum. These membranes,
however, are not called glands, but secreting surfaces.

74 In the oxidations that occur in the body it is not supposed that the
nutrients are immediately converted to carbon dioxide, water, and
urea. On the other hand, it is held that their reduction takes place
gradually, as the reduction of sugar by fermentation, and that the
wastes leaving the body are but the "end products" and show only the
final results.

75 Alcohol, if used in considerable quantity, leads to cirrhosis of the
liver and Bright's disease of the kidneys, both very dangerous
diseases. Dr. William Osler in his treatise, _The Practice of
Medicine_, states that alcohol is the chief cause of cirrhosis of
the liver. Dr. T.N. Bogart, specialist in kidney diseases, asserts
that one third of all the cases of Bright's disease coming under his
observation are caused by alcohol.

76 Hall, _The Purin Bodies_.

77 Review "Main Physiological Problems," page 21.

78 In the production of motion in the body, as well as in the
production of any kind of _purposeful_ motion outside of the body,
three conditions must be fulfilled. There is required, in the first
place, a mechanical device or machine which is so constructed as to
produce a certain kind of motion. In the second place, energy is
needed to operate this device. And, finally, there must be some
controlling force, by means of which the motion is made to
accomplish definite results. The driving of a horse hitched to a
wagon will illustrate these conditions. The wagon is the mechanical
de