770 OF THE FUNCTIONS OF THE NERVOUS SYSTEM. 



to withdraw our attention from those that are accompanied with feelings of pain 

 or discomfort ; and, as the relative intensity of the different Emotional states 

 varies greatly among different individuals, it becomes, as already noticed ( 796), 

 a source of extreme diversity in the formation of all those conclusions by which 

 the conduct of life is directed, and tends to establish certain uniformities of mental 

 action for each individual, which constitute what is termed his " character." 

 But further, we are not to look merely at congenital peculiarities of psychical 

 constitution, as the source of original habitudes of thought ; for as the external 

 conditions in which every individual is placed, differ to a certain extent from 

 those which affect each one of his fellows, so does it happen that, as the deve- 

 lopment of every kind of capacity for mental action is augmented (like the nu- 

 trition of muscle and nerve) by its habitual exercise, the strength of that capacity, 

 and its tendency to exert an active influence on the course of thought, will pa'rtly 

 depend upon the degree in which circumstances call it into play, especially dur- 

 ing the period when, in the natural progress of psychical evolution, it is first 

 taking a prominent share in the operations of the mind. Hence there is a set of 

 acquired habitudes of thought, which, no less than those dependent upon original 

 constitution, determine the consequences of any particular impression upon the 

 " ideational consciousness;" and which thus form part of the "character" of 

 each individual, at any one period of his existence. But the psychical tenden- 

 cies of every one undergo a consecutive change in the progress of life. Infancy, 

 Childhood, Youth, Adolescence, Adult age, the period of Decline, and Senility, 

 have all their characteristic phases of psychical as of physical development and 

 decline ; and this is shown, not merely in the general advance of the intellectual 

 powers up to the period of middle life, and in their subsequent decay, but in a 

 gradual change in the balance of the springs of action which are furnished by 

 the emotional states, the pleasures and pains of each period being (to a certain 

 extent) of a different order from those of every other. This diversity may be 

 partly attributed to changes in the physical constitution; thus, the sexual feeling, 

 which has a most powerful influence on the direction of the thoughts in ado- 

 lescence, adult age, and middle life, has comparatively little effect at the earlier 

 and later periods. So again, the thirst for novelty, and the pleasure in mental 

 activity, which so remarkably characterize the young, when contrasted with the 

 obtuseness to new impressions and the pleasure in tranquil occupations which 

 mark the decline of life, may perhaps be attributed, in part at least, to the greater 

 activity of the changes, both of disintegration and reparation, of which the nerv- 

 ous system (in common with the rest of the organized fabric) is the subject 

 during the earlier part of life, and to its diminished activity as years advance. 

 But there are other changes, which cannot be so distinctly traced to any physical 

 source, but which yet are sufficiently constant in their occurrence, to justify 

 their being regarded as a part of the developmental history of the psychical 

 nature; so that each of the " Seven Ages of Man" has its own character, which 

 may be with difficulty defined in words, but which is recognized by the appre- 

 hension, as it forces itself upon the experience, of every one. 



802. It is universally admitted that, notwithstanding all the obvious diver- 

 sities of Human character and Mental action, there are certain fundamental 

 uniformities which may be traced throughout the whole of this series ; and it 

 is on the basis afforded by these, that the Science of Psychology is erected, to 

 which may be applied, with a mere alteration of form, the definition given of 

 Physiology in the first page of this treatise : " The object of the science of 

 Psychology is to bring together, in a systematic form, the phenomena which nor- 

 mally present themselves during the existence of thinking minds ; and to 

 classify and compare these in such a manner as to deduce from them those gene- 

 ral Laws or Principles which express the conditions of their occurrence, and to 

 determine the causes to which they are attributable." As our present object, 



