hold something deleterious to the thyroid, so
that whole populations in Europe, Asia and America drinking such water
have become goitrous and cretinous, and a large percentage straight
imbeciles. Endemic cretinism is the name given to the condition. In
parts of Switzerland, Savoy, Tyrol and the Pyrenees, in America
around some of the Great Lakes, there are still such foci. Marco Polo
described similar areas he encountered in his travels through Asia.

Certain foods with aphrodisiac qualities may act by stimulating the
internal secretion of the sex glands. A type of pituitocentric has an
almost uncontrollable craving for sweets. Alcohol and the endocrines
remain to be studied.

Light, heat and humidity stand in some special relation to the
adrenals. Pigment deposit in the skin as protection against light
is controlled by the adrenal cortex. The reaction of the skin blood
vessels to heat and humidity is regulated by the adrenal medulla. A
change in the adrenal as a response to changes of temperature and
humidity in an environment would result in a number of concomitant
transformations throughout the body. So variation and adaptation are
probably connected. Most Europeans living for a sufficiently long time
in the tropics suffer from a combination of symptoms spoken of as
"Punjab head" or "Bengal head." The condition is probably the result
of excessive adrenal stimulation by the excessive heat and light of
the tropical sun, followed by a reaction of exhaustion and failure,
with the consequent phenomena of a form of neurasthenia. In the
section on the pineal gland there was mentioned the relation between
light and the pineal gland in growing animals, and how it serves to
keep in check the sex-stimulating action of light. The earlier puberty
and menstruation of the warmer climates may be explained as due to an
earlier regression of the pineal under the pressure of a great amount
of light playing upon the skin.

All these, and many more could be cited, are instances of the direct
influence of environmental factors upon one or more of the endocrines,
and so upon the organism as a whole. Indeed, stimuli may be considered
to modify an organism only in so far as they modify the glands of
internal secretion. Consequently, climatic factors will tend to make a
population possess certain points of resemblance in common.

Varieties of the human race exist as do varieties of dogs. The
pekingese and the fox terrier are as different