THE LAWS OF HABIT. 439 



ties of mental action, which are so entirely conformable to those 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, the latter in terms of brain — the universally admitted 

 fact that any sequence of mental action which has been frequently 

 repeated tends to perpetuate itself ; so that we find ourselves auto- 

 matically prompted to thinJc, feel, or do what we have been before 

 accustomed to think, feel, or do, under like circumstances, without any 

 consciously formed purpose, or anticipation of results. For there is no 

 reason to regard the cerebrum as an exception to the general principle 

 that, while each part of the organism tends to form itself in accord- 

 ance with the mode in which it is habitually exercised, this tendency 

 will be especially strong in the nervous apparatus, in virtue of that 

 incessant regeneration which is the very condition of its functional 

 activity. It scarcely, indeed, admits of doubt that every state of 

 ideational consciousness which is either very strong or is habitually 

 repeated, leaves an organic impression on the cerebrum ; in virtue of 

 which that same state may be reproduced at any future time, in respond- 

 ence to a suggestion fitted to excite it. . . . The ' strength of early 

 association ' is a fact so universally recognized, that the expression of 

 it has become proverbial ; and this precisely accords with the physio- 

 logical principle that, during the period of growth and development, 

 the formative activity of the brain will be most amenable to directing 

 influences. It is in this way that what is early ' learned by heart ' 

 becomes branded in (as it were) upon the cerebrum ; so that its ' traces ' 

 are never lost, even though the conscious memory of it may have com- 

 pletely faded out. For, when the organic modification has been once 

 fixed in the growing brain, it becomes a part of the normal fabric, and 

 is regularly maintained by nutritive substitution ; so that it may 

 endure to the end of life, like- the scar of a wound." 



Dr. Carpenter's phrase, that our nervous system groics to the modes 

 hi which it has been exercised expresses the philosophy of habit in a 

 nutshell. We may now trace some of the practical applications of the 

 principle to human life. 



The first result of it is that habit simplifies the movements required 

 to achieve a given result, makes them more accurate and diminishes 

 fatigue. 



" The beginner at the piano not only moves his finger up and 

 down in order to depress the key, he moves the whole hand, the fore- 

 arm, and even the entire body, especially moving its least rigid part, 

 the head, as if he would press down the key with that organ too. 

 Often a contraction of the abdominal muscles occurs as well. Prin- 

 cipally, however, the impulse is determined to the motion of the hand 

 and of the single finger. This is, in the first place, because the move- 



