they soon
voluntarily practice it. We may frequently see a person voluntarily
raising his eyebrows to express surprise, or smiling to express
pretended satisfaction and acquiescence. A man often wishes to make
certain gestures conspicuous or demonstrative, and will raise his
extended arms with widely opened fingers above his head to show
astonishment or lift his shoulders to his ears to show that he cannot or
will not do something.

We have seen that the study of the theory of expression confirms to a
certain limited extent the conclusion that man is derived from some
lower animal form, and supports the belief of the specific or
subspecific unity of the several races; but as far as my judgment
serves, such confirmation was hardly needed. We have also seen that
expression in itself, or the language of the emotions, as it has
sometimes been called, is certainly of importance for the welfare of
mankind. To understand, as far as is possible, the source or origin of
the various expressions which may be hourly seen on the faces of the men
around us, not to mention our domesticated animals, ought to possess
much interest for us. From these several causes we may conclude that the
philosophy of our subject has well deserved that attention which it has
already received from several excellent observers, and that it deserves
still further attention, especially from any able physiologist.

3. Blushing[140]

Blushing is the most peculiar and the most human of all expressions.
Monkeys redden from passion, but it would require an overwhelming amount
of evidence to make us believe that any animal could blush. The
reddening of the face from a blush is due to the relaxation of the
muscular coats of the small arteries, by which the capillaries become
filled with blood; and this depends on the proper vasomotor center being
affected. No doubt if there be at the same time much mental agitation,
the general circulation will be affected; but it is not due to the
action of the heart that the network of minute vessels covering the face
becomes under a sense of shame gorged with blood. We can cause laughing
by tickling the skin, weeping or frowning by a blow, trembling from the
fear of pain, and so forth; but we cannot cause a blush by any physical
means--that is, by any action on the body. It is the mind which must be
affected. Blushing is not only involuntary, but the wish to restrain it,
by leading to self-attention, actually increases th