MODES OF ACTION OF NERVOUS SYSTEM. 349 
(§ 194) and Respiration (§ 340)—2. If the ganglionic centre 
to which the impression is conveyed, should be one through 
which the consciousness is necessarily affected, sensation be- 
comes a necessary link in the circular chain ; and the action 
is distinguished as consensual, or “ sensori-motor.” The closing 
and opening of the pupil of the eye, in accordance with the 
amount of light that falls upon the retina, together with other 
remarkable adjustments which are involuntarily made in the 
working of that wonderful organ, are characteristic examples 
of this class. In the foregoing operations no mental change 
higher than simple consciousness of impressions—that is to 
say, Sensation, with which may be blended the simple feelings 
of pleasure and pain—is involved. Such would appear to be 
the condition of the Human infant on its first entrance into 
the world, before the self-education of its higher faculties has 
commenced ; and such is probably the state of Invertebrated 
animals generally, whose instinctive actions seem to be refer- 
able to one or other of the foregoing classes. 
431. But Sensation is the very lowest form of purely 
Mental action. When the outness or externality of the 
objects which give rise ta our sensations has been recognised 
by perception, we begin to form ideas respecting their nature, 
qualities, &c. ; and it is in the various processes of association, 
‘comparison, &e., to which these ideas are subjected, that our 
Reasoning faculty consists. Now these processes may go on 
in great degree automatically, that is, without any control or 
guidance on our own part, as happens in the states of Dream- 
ing, Reverie, and Abstraction ; and they may express them- 
selves in action, as we see in the movements of a Somnambulist, 
who may be said to be acting his dreams. This form (3) of 
Nervous activity, which may be termed ideo-motor, seems to be 
the ordinary mode in such of the lower animals as are governed 
by Intelligence rather than by instinct (Chap. x1v.); but it is 
abnormal and exceptional in Man.— With ideas are associated 
clings of various kinds, which constitute Passions and Emo- 
s; and these (4), when strongly excited, may become direct 
gs of action, so powerful as even to master the control of 
e ol producing emotional movements. 
_ 432. In the well-regulated mind of Man, however, the Will 
2) possesses supreme direction over the whole current of 
ught, feeling, and action: regulating the succession of the 
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