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Show 28 THE PRINCIPLE OF CnAT'. f. that probably all will hel'eafter be found to co1ne under the same or closely analogous heads. I need hardly premise .that 1noven1ents or changes in any part of t.ho body,-as the wagging of a dog's tail, the drawing back of a horse's ears, the shrugging of a man's shoulders, or the dilatation of the capillary vessels of the skin,-1nay all equally well serve for expression. Tho three Principles are as follows. I. The principle of serviceable associatecl Habits.Oertain con1plex actions are of direct or indirect service under certain states of the mind, h1 order to relieve or gratify certain sensations, desires, &c. ; and whenever the same state of mind is induced, however feebly, there is a tendency through the force of habit and association for the same 1noveme1~ts to be performed, though they may not then be of the least use. Some actions ordinarily associated through habit with certain states of the mind rnay be partially repressed through the will, and in such cases the n1uscles which are least under the separate control of the wHl are the most liable still to act, causing movements which we recognise as expressive. In certain other cases the checking of one habitual movetnent requires other sHght move· 1nents; and these are like,--vise expressive. II. The principle of Antithesis.-Oertain states of the 1nind lead to certain habitual actions, which are of service, as under our first principle. Now when a directly opposite state of mind is induced, there is a strong and in voluntary tendency to the performance of n1ovements of a directly opposite nature, though these are of no use; and such move1nents are in some cases highly expressive. III. The principle of actions due to the constitution of the Nervous Systmn, independently from~ the first of the Will, and independently to a certain ewtent of Habit.- SEUVIC:lnABtE ASSOCIA1'ED HABl'rB. 29 vVhen the sensorium is strongly excited, nerve-force is generated in excess, and is transmitted in certain definite directions, depending on the connection of the nerve-cells, and partly on habit: or the supply of nerve-force may, as it appears, be interrupted. Effects are thus produced which we recognise as expressive. ~rhis third principle may, for the sake of brevity, be called that of the direct action of the nervous system. vVith respect to our first Principle, it is notorious how powerful is the force of habit. 'rhe 1nost complex . and difficult movements can in time be performed without the least effort or consciousness. It is not positively known ·how it comes that habit is so efficient in ii1cilitnting co1nplex n1ovements · but physiolo()'ists . ' h adtnit 2 ''that the conducting power of the nervous " fibres increases with the frequency of their excite" 1nent." This applies to the nerves of 1notion and sensation, as well as to those connected with the act of thinking. That some physical change is produced in the nerve-cells or nerves which are habitually used can hardly be doubted, for otherwise it is impossible to understand how the tendency to certain acquired movelnents is inherited. That they are inherited we see with horses in certain transmitted paces, such as cantering and ambling, which are not natural to them,in the pointing of young pointers and the setting of young setters-in the peculiar manner of flight of c rtain breeds of the pigeon, &c. We havo analogons cases with mankind in the inheritance of tricks or unusual gestures, to which we shall presently rec nl'. 2 MiUler, ' Elements of Physiology,' Eng. tmnslat. vol. ii. p. 93!). Sec also Mr. H. Spencer's intercstiug speculations on the same subject, aud on tho genesis of nerves, in hi~ ' Principles of Biology,' vol. ii. P· :146 i and in l1i~ 'Priuciplc~ of I :;ycholosy,' 2nd c<.lit. pp. 511-557. |