age reaction time. The experiment may be repeated
with boys only and then with girls, comparing their average reaction time.

*Reflex Action of the Salivary Glands.*--Place a small pinch of salt upon
the tongue and note the flow of saliva into the mouth. Try other
substances, as starch, bits of wood, and sugar. What appears to be the
natural stimulus for these glands? Compare with reflex actions of the
muscles.

CHAPTER XIX - HYGIENE OF THE NERVOUS SYSTEM

The far-reaching effects and serious nature of disorders of the nervous
system are sufficient reasons for considering carefully those conditions
that make or mar its efficiency. Controlling all the activities of the
body and affecting through its own condition the welfare of all the
organs, the hygiene of the nervous system is, in a large measure, the
hygiene of the entire body. Moreover, it is known that some of our worst
diseases, including paralysis and insanity, are disorders of the nervous
system and are prevented in many instances by a proper mode of living.

*The Main Problem.*--Many of our nervous disorders are undoubtedly due to
the age in which we live. Our modern civilization, with all its facilities
for human advancement and enjoyment, throws an extra strain upon the
nervous system. Educational and social standards are higher than ever
before and life in all its phases is more complex. Since we can hardly
change the conditions under which we live, and probably would not if we
could, we must learn to adapt or adjust ourselves to them so as to secure
for the nervous system such relief as it requires. This adjustment is
sometimes difficult, even when the actual needs of the nervous system are
known.

The healthful action of the nervous system requires, on the one hand,
exercise, but on the other hand, a certain condition of quietude, or
_poise_--a state which is directly opposed to that of restlessness. The
conditions of modern life seem able to force upon the nervous system all
the exercise that it needs, and more (whether it be of the right kind or
not), so that the main problem of to-day seems to be that of conserving,
or economizing, the nervous energy and of preventing nervous waste.

*Wasteful Forms of Nervous Activity.*--There are without doubt many forms
of activity that waste the vital forces of the body and lead to nervous
exhaustion. Take, for example, the rather common habit of worrying over
the trivial things of life. Certainly the n