478 OF THE NERVOUS SYSTEM AND ITS ACTIONS. 



strongest efforts of the will to restrain them ; as when laughter is 

 provoked by some ludicrous sight or sound, or by the remembrance of 

 such, at an unseasonable time. It is probable, from the strong mani- 

 festations of emotion exhibited by many of the lower animals, that 

 some of the actions which we assemble under the general designation 

 of instinctive, are to be referred to this group. 



846. There are many sensations, however, which do not thus imme- 

 diately give rise to muscular movements ; their operation being rather 

 that of stimulating to action the Intellectual powers. There can be 

 little doubt that all Mental processes are dependent, in the first instance, 

 upon Sensations, which serve to the Mind the same kind of purpose 

 that food and air fulfil in the economy of the body. If we could 

 imagine a being to come into the world with its mental faculties fully 

 prepared for action, but destitute of any power of receiving sensations, 

 these faculties would never be aroused from the condition in which they 

 are in profound sleep ; and the being must remain in a state of com- 

 plete unconsciousness, because there is nothing of which it can be made 

 conscious, no kind of idea which can be aroused within it. But after 

 the mind has once been in active operation, the destruction of all future 

 power of receiving sensations would not reduce it again to the inactive 

 condition. For sensations are so stored up in the mind by the power 

 of Memory, that they may give rise to ideas at any future time ; and 

 thus the mind may feed, as it were, upon the past. Now the ideas 

 which are excited by sensations, and which are coloured by the state of 

 Feeling which accompanies them, become the subjects of Reasoning 

 processes . more or less complex, sometimes of the utmost brevity and 

 simplicity, sometimes of the most refined and intricate nature. These 

 reasoning processes, when they result in a determination to execute a 

 particular movement, execute that movement by an act of Volition ; 

 the peculiar character of which is that it is the expression of a definite 

 purpose, of a designed adaptation of means to ends, on the part of the 

 individual performing it, instead of being the result of the mere blind, 

 indiscriminating impulse which seems to be the mainspring of the 

 instinctive operations. It is in Man that we find the highest develop- 

 ment of the reasoning faculties ; but it is quite absurd to limit them to 

 him, as some have done, since no impartial observer can doubt that 

 many of the lower animals can execute reasoning processes, as complete 

 in their way as those of Man, though much more limited in their scope. 



847. Thus, then, we have to consider the Nervous system under four 

 heads ; first, as the instrument of the Reflex actions ; second, as the 

 instrument of the Consensual actions ; third, as the instrument of the 

 Emotional actions ; and fourth, as the instrument of the Intellectual 

 processes and of Voluntary movements. There is reason to believe 

 that the Nervous Centre from which the muscles derive their impulse to 

 contract, is the same, whether the movement be prompted by an impres- 

 sion which does not excite the consciousness, by a sensation, by an 

 emotion, or by a volition; and that this instrument may be played upon, 

 so to speak, by other centres, which minister to these functions respec- 

 tively. In order that the relations of the component parts of the 

 Nervous apparatus may be better understood, it will be desirable to 



