MODES OF ACTION OF NERVOUS SYSTEM. 349 



( 194) and Eespiration ( 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 to 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, &c., 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, xiv.) ; but it is 

 abnormal and exceptional in Man. With ideas are associated 

 feelings of various kinds, which constitute Passions and Emo- 

 tions; and these (4), when strongly excited, may become direct 

 springs of action, so powerful as even to master the control of 

 the Will, producing emotional movements. 



432. In the well-regulated mind of Man, however, the Will 

 (5) possesses supreme direction over the whole current of 

 thought, feeling, and action : regulating the succession of the 



