mind. The idiot
lacks power of attention. The maniac lacks control of his attention.
The deluded lacks grasp and flexibility of attention. The crank can
only attend to one thing. The old man is feeble in the attention,
having lost his hold. So it goes. The attention is the instrument of
the one sort of normal mental activity called Apperception, and so
impairment of the attention shows itself at once in some particular
form of defect.

Third, it is interesting to know that in progressive mental failure
the loss of the powers of the mind takes place in an order which is
the reverse of that of their original acquisition. The most complex
functions, which are acquired last, are the first to show impairment.
In cases of general degeneration, softening of the brain, etc., the
intelligence and moral nature are first affected, then memory,
association, and acquired actions of all sorts, while there remain,
latest of all, actions of the imitative kind, most of the deep-set
habits, and the instinctive, reflex, and automatic functions, This
last condition is seen in the wretched victim of dementia and in the
congenital idiot. The latter has, in addition to his life processes
and instincts, little more than the capacity for parrot-like
imitation. By this he acquires the very few items of his education.

The recovery of the patient shows the same stages again, but in the
reversed direction; he pursues the order of the original acquisition,
a process which physicians call Re-evolution.

CHAPTER VI.

HOW WE EXPERIMENT ON THE MIND--EXPERIMENTAL PSYCHOLOGY.

In recent years the growth of the method of experimenting with bodies
in laboratories in the different sciences has served to raise the
question whether the mind may not be experimented with also. This
question has been solved in so far that psychologists produce
artificial changes in the stimulations to the senses and in the
arrangements of the objects and conditions existing about a person,
and so secure changes also in his mental states. What we have seen of
Physiological Psychology illustrates this general way of proceeding,
for in such studies, changes in the physiological processes, as in
breathing, etc., are considered as causing changes in the mind. In
Experimental Psychology, however, as distinguished from Physiological
Psychology, we agree to take only those influences which are outside
the body, such as light, sound, temperature, etc., keeping the subject