THE LAWS OF HABIT. 



435 



pain and cold, than are the neighboring parts. A sprained ankle, a 

 dislocated arm, are in danger of being sprained or dislocated again ; 

 joints that have once been attacked by rheumatism or gout, mucous 

 membranes that have been the seat of catarrh, are with each fresh re- 

 currence more prone to a relapse, until often the morbid state chron- 

 ically substitutes itself for the sound one. And if we ascend to the 

 nervous system, we find how many so-called functional diseases seem 

 to keep themselves going simply because they happen to have once 

 begun ; and how the forcible cutting short by medicine of a few at- 

 tacks is often sufficient to enable the physiological forces to get posses- 

 sion of the field again, and to bring the organs back to functions of 

 health. Epilepsies, neuralgias, convulsive affections of various sorts, 

 insomnias, are so many cases in point. And, to take what are more 

 obviously habits, the success with which a " weaning " treatment can 

 often be applied to the victims of unhealthy indulgence of passion, or 

 of mere complaining or irascible disposition, shows us how much the 

 morbid manifestations themselves were due to the mere inertia of the 

 nervous organs, when once launched on a false career. 



Can we now form a notion of what the inward physical changes 

 may be like, in organs whose habits have thus struck into new paths ? 

 In other words, can we say just what mechanical facts the expression 

 " change of habit " covers when it is applied to a nervous system ? 

 Certainly we can not in anything like a minute or definite way. But 

 our usual scientific custom of interpreting hidden molecular events 

 after the analogy of visible massive ones enables us to frame easily an 

 abstract and general scheme of processes which the physical changes 

 in question may be like. And when once the possibility of some kind 

 of mechanical interpretation is established, Mechanical Science, in her 

 present mood, will not hesitate to set her brand of ownership upon 

 the matter, feeling sure that it is only a question of time when the 

 exact mechanical explanation of the case shall be found out. 



Of course, a simple habit, like every other nervous event — the habit 

 of snuffling, for example, or of putting one's hands into one's pockets, 

 or of biting one's nails — is, mechanically, nothing but a reflex dis- 

 charge ; and its anatomical substratum must be a reflex arc in the 

 nervous system. The more complex habits, as we shall presently see 

 more fully, are, from the same neural point of view, nothing but con- 

 catenated discharges in the nerve-centers, due to the presence there of 

 systems of reflex arcs, so organized as to wake each other up succes- 

 sively — the impression produced by one muscular contraction serving 

 as a stimulus to provoke the next, until a final impression inhibits 

 the process and closes the chain. The mechanical problem, then, is to 

 explain the formation de novo of a simple reflex arc in a pre-existing 

 nervous system. Here, as in so many other cases, it is only the pre- 

 mier pas qui cottte. For a nervous system is nothing but a system of 

 paths which the nerve-current follows, between a sensory terminus a 



