HABIT. 105 



its integrity, and be not disrupted when its structure yields. 

 The change of structure here spoken of need not involve 

 the outward shape ; it may be invisible and molecular, as 

 when a bar of iron becomes magnetic or crystalline through 

 the action of certain outward causes, or India-rubber 

 becomes friable, or plaster * sets.' All these changes are 

 rather slow ; the material in question opposes a certain 

 resistance to the modifying cause, which it takes time to 

 overcome, but the gradual yielding whereof often saves the 

 material from being disintegrated altogether. When the 

 structure has yielded, the same inertia becomes a condition 

 of its comparative permanence in the new form, and of the 

 new habits the body then manifests. Plasticity, then, in 

 the wide sense of the word, means the possession of a struc- 

 ture weak enough to 3'ield to an influence, but strong 

 enough not to yield all at once. Each relatively stable 

 phase of equilibrium in such a structure is marked by 

 what we may call a new set of habits. Organic matter, 

 especially nervous tissue, seems endowed with a very ex- 

 traordinary degree of plasticity of this sort; so that we 

 may without hesitation lay down as our first proposition 

 the following, that t]m jphenomena of habit in living beings are 

 due to the plasticity* of the organic materials of lohich their 

 bod ies are composed . 



But the philosophy of habit is thus, in the first instance, 

 a chapter in physics rather than in physiology or psychol- 

 ogy. That it is at bottoiii a physical principle is admitted 

 by all good recent writers on the subject. They call atten- 

 tion to analogues of acquired habits exhibited by dead mat- 

 ter. Thus, M. Leon Dumont, whose essay on habit is per- 

 haps thp most philosophical account yet published, writes : 



" Every one knows how a garment, after having been worn a certain 

 time, clings to the shape of the body better than when it was new; 

 there has been a change in the tissue, and this change is a new habit of 

 cohesion. A lock works better after being used some time; at the out- 

 set more force was required to overcome certain roughnesses in the 

 mechanism. The overcoming of their resistance is a phenomenon of 

 habituation. It costs less trouble to fold a paper when it has been 



* lu the sense above explained, which applies to inner structure as well 

 as to outer form. 



