800 OF THE FUNCTIONS OF THE NERVOUS SYSTEM. 



happens that we mispronounce or misspell a word, by introducing into it a 

 portion of some other whose turn is shortly to come, its place in the sentence 

 which is in process of formation being a little further on; or it may be that 

 the whole of the anticipated word is substituted for the one which ought to 

 have been expressed. Now it is obvious that there could be neither any con- 

 sciously formed intention of breaking the regular sequence, nor any volitional 

 effort to do so; and the result is evidently due to the superior vividness with 

 which the idea of the anticipated word is present to the mind, as compared with 

 that of the word which the course of construction requires. It is the dominant 

 idea, then, which determines the movement, the Will simply permitting it ; 

 and the more completely the Volitional power is directed to other objects, the 

 more completely automatic are the actions of this class. They may, indeed, 

 come to be performed even without the consciousness, or at least without the 

 remembered consciousness, of the agent ; as we see in the case of those who 

 have the habit of " thinking aloud," and who are subsequently quite surprised 

 on learning what they have uttered. The one-sided conversation of some 

 persons, who are far more attentive to their own trains of thought, than they 

 are to what may be expressed by others, and who are allowed to proceed with 

 little or no interruption, is often a sort of " thinking aloud." 1 All that is 

 here stated is in perfect accordance with the general principle already laid down 

 ( 683), that in proportion as the higher channels of activity are obstructed, 

 will the excitation of nerve-force manifest itself through the lower. For, 

 whilst the ordinary sequence is for external impressions to excite sensations, 

 for sensations to excite ideas, and for ideas (after becoming the subject of 

 reasoning processes of greater or less complexity) to issue in volitional deter- 

 minations, the direct action of ideational changes in the Cerebrum on the 

 motor system, when either the Will is in abeyance or is entirely directed to 

 mental operations, seems quite as natural as the immediate reaction of sensa- 

 tional changes through the Sensory ganglia, or of impressional changes through 

 the Spinal Cord. 



827. The phenomena of Somnambulism are no less important in a scientific 

 point of view, when they are regarded under the same aspect. They differ from 

 those already described, in that they occur in a state of consciousness so far distinct 

 from the ordinary waking condition, as not to be connected with it by the ordi- 

 nary link of Memory; and although the course of thought in Somnambulism 

 usually manifests the directing influence of previous habits, and the knowledge 

 of persons and things possessed during the waking state may be readily brought 

 before the mind, yet nothing which occurs during the state of Somnambulism 

 is ever retraced spontaneously, or can be brought back by an act of recollection. 

 Impressions upon the nervous system, however, are sometimes left by strong 

 emotional excitement, which give rise to subsequent feelings of discomfort, of 

 whose origin the individual is entirely unconscious. 3 The phenomena of Som- 

 nambulism are so various, that it is difficult to give any general definition that 

 shall include the whole ; but it is a condition which is common to all forms of 

 this state, that the controlling power of the Will over the current of thought 

 is entirely suspended, and that all the actions are directly prompted by the ideas 

 which possess the mind ; and the differences chiefly arise out of the mode in 

 which the succession of ideas is directed, this being in some cases a coherent 

 sequence through the whole of which some one dominant impression may be 

 traced, whilst in other instances it is more or less completely determinable by ex- 



1 This was pre-eminently the case with Coleridge, whose peculiar habits have been 

 already noticed, $ 817, note. 



2 See a very curious example of this kind, which fell under the author's own observa- 

 tion, narrated in the Article "Sleep," in the "Cyclop, of Anat. and Phys.," vol. iv. 

 p. 693. 



