HABIT. Ill 



production of new tissue, than it is to the eye of sense that such repa- 

 ration supplies an actual loss of substance by disease or injury. 



"Now, in this constant and active reconstruction of the nervous 

 system, we recognize a most marked conformity to the general plan 

 manifested in the nutrition of the organism as a whole. For, in the 

 first place, it is obvious that there is a tendency to the production of a 

 determinate type of structure ; which type is often not merely that of 

 the species, but some special raodifleation of it which characterized one 

 or both of the progenitors. But this type is peculiarly liable to modi- 

 fication during the early period of life ; in which the functional activity 

 of the nervous system (and particularly of the brain) is extraordinarily 

 great, and the reconstructive process proportionally active. And this 

 modiflability expresses itself in the formation of the mechanism by 

 which those secondarily automatic modes of movement come to be 

 established, which, in man, take the place of those that are congenital 

 in most of the animals beneath him ; and those modes of sense-percep- 

 tion come to be acquired, which are elsewhere clearly instinctive. For 

 there can be no reasonable doubt that, in both cases, a nervous 

 mechanism is developed in the course of this self-education, correspond- 

 ing with that which the lower animals inherit from their parents. The 

 plan of that rebuilding process, which is necessary to maintain the 

 integrity of the organism generally, and which goes on with peculiar 

 activity in this portion of it, is thus being incessantly modified ; and in 

 this manner all that portion of it which ministers to the external life of 

 sense and motion that is shared by man with the animal kingdom at 

 large, becomes at adult age the expression of the habits which the 

 individual has acquired during the period of growth and development. 

 Of these habits, some are common to the race generally, while others 

 are peculiar to the individual ; those of the former kind (such as walk- 

 ing erect) being universally acquired, save where physical inability 

 prevents ; while for the latter a special training is needed, which is 

 usually the more effective the earlier it is begun — as is remarkably 

 seen in the case of such feats of dexterity as require a conjoint edu- 

 cation of the perceptive and of the motor powers. And when thus 

 developed during the period of growth, so as to have become a part of 

 the constitution of the adult, the acquired mechanism is thenceforth 

 maintained in the ordinary course of the nutritive operations, so as to 

 be ready for use when called upon, even after long inaction. 



"What is so clearly true of the nervous apparatus of animal life can 

 scarcely be otherwise than true of that which ministers to the automatic 

 activity of the mind. For, as already shown, the study of psychology 

 has evolved no more certain result than that there are uniformities of 

 mental action which are soentirely confoi'mable tothose of bodily action 

 as to indicate their intimate relation to a ' mechanism of thought and 

 feeling,' acting under the like conditions with that of sense and motion. 

 The psychical principles of association, indeed, and the physiological 

 principles of nutrition, simply express— the former in terms of mind, 



