gled with a free volatile acid, are also
found in the perspiration. It is the acid which imparts to this
secretion its peculiar odor, and acid reaction. The process of its
secretion is continuous, but, like all bodily functions, it is subject
to influences which augment or retard its activity. If, as is usually
the case when the body is in a state of repose, evaporation prevents its
appearance in the _liquid_ form, it is called _invisible_ or _insensible
perspiration_. When there is unusual muscular activity, it collects upon
the skin, and is known as _sensible perspiration_. This secretion
performs an important office in the animal economy, by maintaining the
internal temperature at about 100 deg. Fahr. Even in the Arctic regions,
where the explorer has to adapt himself to a temperature of 40 deg. to 80 deg.
below zero, the generation of heat in the body prevents the internal
temperature from falling below this standard. On the contrary, if the
circulation is quickened by muscular exertion, the warmer blood flowing
from the internal organs into the capillaries, raises the temperature of
the skin, secretion is augmented, the moisture exudes from the pores,
and perceptible evaporation begins. A large portion of the animal heat
is thrown off in this process, and the temperature of the skin is
reduced. A very warm, dry atmosphere can be borne with impunity but if
moisture is introduced, evaporation ceases, and the life of the animal
is endangered. Persons have been known to remain in a temperature of
about 300 deg. Fahr. for some minutes without unpleasant effects. Three
conditions may be assigned as effective causes in retarding or
augmenting this cutaneous secretion, variations in the temperature of
the atmosphere, muscular activity, and influences which affect the
nerves. The emotions exert a remarkable influence upon the action of the
perspiratory glands. Intense fear causes great drops of perspiration to
accumulate on the skin, while the salivary glands remain inactive.

TEARS. The lachrymal glands are small lobular organs, situated at the
outer and upper orbit of the eye, and have from six to eight ducts,
which open upon the conjunctiva, between the eyelid and its inner fold.
This secretion is an alkaline, watery fluid. According to Dr. Dalton,
its composition is as follows:

Water, 882.0
Albuminous matter, 5.0
Chloride of Sodium, 13.0
Mineral Salts, a trace,