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HEN we look at living creatures from an outward point of view,



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habits. In wild animals, the usual round of daily behavior seems a
necessity implanted at birth; in animals domesticated, and especially
in man, it seems, to a great extent, to be the result of education.
The habits to which there is an innate tendency are called instincts;
some of those due to education would by most persons be called acts
of reason. It thus appears that habit covers a very large part of life,
and that one engaged in studying the objective manifestations of mind mind us
is bound at the very outset to define clearly just what its limits are.
The moment one tries to define what habit is, one is led to the
fundamental properties of matter. The laws of Nature are nothing
but the immutable habits which the different elementary sorts of
matter follow in their actions and reactions upon each other. In the
organic world, however, the habits are more variable than this. Even distingu
instincts vary from one individual to another of a kind; and are modi-n part
fied in the same individual, as we shall later see, to suit the exigencies

of the case.
The habits of an elementary particle of matter can not
change (on the principles of the atomistic philosophy), because the
particle is itself an unchangeable thing; but those of a compound
mass of matter can change, because they are in the last instance due
to the structure of the compound, and either outward forces or inward
tensions can, from one hour to another, turn that structure into some-
thing different from what it was. That is, they can do so if the body
be plastic enough to maintain 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

VOL. XXX.-28


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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 structure weak enough to yield 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 extraordinary degree of plasticity of this sort; so that we may without hesitation lay down as our first proposition the following, that the phenomena of habit in living beings are due to the plasticity* of the organic materials of which their bodies are composed.


But the philosophy of habit is thus, in the first instance, a chapter in physics rather than in physiology or psychology. That it is at bottom a physical principle is admitted by all good recent writers on the subject. They call attention to analogues of acquired habits exhibited by dead matter. Thus, M. Léon Dumont, whose essay on habit is perhaps the 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 outset 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 folded already. This saving of trouble is due to the essential nature of habit, which brings it about that, to reproduce the effect, a less amount of outward causality is required. The sounds of a violin improve by use in the hands of an able artist, because the fibers of the wood at last contract habits of vibration conformed to harmonic relations. This is what gives such inestimable value to instruments that have belonged to great masters. Water in flowing hollows out for itself a channel, which grows broader and deeper, and, after having ceased to flow, it resumes, when it flows again, the path traced by itself before. Just so, the impressions of outer objects fashion for themselves in the nervous system more and more appropriate paths, and these vital phenomena recur under similar excitements from without, when they have been interrupted a certain time."

Not in the nervous system alone. A scar anywhere is a locus minoris resistentice, more liable to be abraded, inflamed, to suffer

* In the sense above explained, which applies to molecular structure as well as to that of grosser parts.

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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 recurrence more prone to a relapse, until often the morbid state chronically 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 attacks is often sufficient to enable the physiological forces to get posses6sion 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 e morbid manifestations themselves were due to the mere inertia of the at nervous organs, when once launched on a false career.


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

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et 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 3 exact mechanical explanation of the case shall be found out.

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Of course, a simple habit, like every other nervous event-the habit e of snuffling, for example, or of putting one's hands into one's pockets, 1 or of biting one's nails-is, mechanically, nothing but a reflex dist charge; and its anatomical substratum must be a reflex arc in the T nervous system. The more complex habits, as we shall presently see 3 more fully, are, from the same neural point of view, nothing but concatenated discharges in the nerve-centers, due to the presence there of r systems of reflex arcs, so organized as to wake each other up successively-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 premier pas qui coûte. For a nervous system is nothing but a system of paths which the nerve-current follows, between a sensory terminus a

quo and a muscular, glandular, or other terminus ad quem. A path once traversed by a nerve-current might be expected to follow the law of most of the paths we know,* and to be scooped out and made more permeable than before; and this ought to be repeated with each new passage of the current. Whatever obstructions may have kept it at first from being a path, should then, little by little, and more and more, be swept out of the way, until at last it might become a natural drainage-channel. This is what happens where either solids or liquids pass over a path; there seems no reason why it should not happen where the thing that passes is not a moving body, but a mere wave of rearrangement in matter that does not displace itself in the line of the "path," but merely changes chemically or turns itself round in place, or vibrates across the line. The most plausible views of the nerve-current make it out to be the passage of some such wave of rearrangement as this. If only a part of the matter of the path were to "rearrange " itself, the neighboring parts remaining inert, it is easy to see how their inertness might oppose a friction which it would take many waves of rearrangement to break down and overcome. If we call the path itself the "organ," and the rearrangement of the molecules the " 'function," then it is obviously a case for repeating the celebrated French formula of "La fonction fait l'organe."

So nothing is easier than to imagine how, when a current once has traversed a path, it should traverse it more readily still a second time. But what made it ever traverse it the first time? In answering this question we can only fall back on our general conception of a nervous system as a mass of matter whose parts, constantly kept in states of different tension, are as constantly tending to equalize their states. The equalization between any two points occurs through whatever path may at the moment be most pervious. But, as a given point of the system may belong, actually or potentially, to many different paths, and, as the play of nutrition is subject to accidental changes, blocks may from time to time occur, and make currents shoot through unwonted lines. Such an unwonted line would be a new-created path, which, if traversed repeatedly, would become the beginning of a new reflex arc. All this is vague to the last degree, and amounts to little more than saying that a new path may be formed by the sort of chances that in nervous material are likely to occur. But, vague as it is, it is really the last word of our wisdom in the matter.‡

*Some paths, to be sure, are banked up by bodies moving through them under too great pressure, and made impervious. These special cases we disregard.

We can not say the will, for, though many, perhaps most, human habits were once voluntary actions, no action can be primarily such. While an habitual action may once have been voluntary, the voluntary action must before that, at least once, have been impulsive or reflex. It is this very first occurrence of all that we consider in the text.

Those who desire a more definite formulation may consult J. Fiske's "Cosmic Philosophy," vol. ii, pp. 142-146, and Spencer's "Principles of Biology," sections 302 and 303, and the part entitled "Physical Synthesis" of his "Principles of Psychology." Mr.

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It must be noticed that the growth of structural modification in living matter may be more rapid than in any lifeless mass, because the incessant nutritive renovation of which the living matter is the seat, tends often to corroborate and fix the impressed modification, rather than to counteract it by renewing the original constitution of the tissue that has been impressed. Thus, we notice after exercising our muscles or our brain in a new way, that we can do so no longer at that time; but after a day or two of rest, when we resume the discipline, our increase in skill not seldom surprises us. This has led a German author to say that we learn to swim during the winter and to skate during the summer.

Dr. Carpenter writes: "It is a matter of universal experience, that every kind of training for special aptitudes is both far more effective, and leaves a more permanent impress, when exerted on the growing organism, than when brought to bear on the adult. The

effect of such training is shown in the tendency of the organ to'grow open,


to' the mode in which it is habitually exercised; as is evidenced by the increased size and power of particular sets of muscles, and the extraordinary flexibility of joints, which are acquired by such as have been early exercised in gymnastic performances. . . . There is no part of the organism of man in which the reconstructive activity is so great, during the whole period of life, as it is in the ganglionic substance of the brain. This is indicated by the enormous supply of blood which it receives. It is, moreover, a fact of great significance that the nerve-substance is specially distinguished by its reparative power. For while injuries of other tissues (such as the muscular) which are distinguished by the speciality of their structure and endowments, are repaired by substance of a lower or less specialized type, those of nerve-substance are repaired by a complete reproduction of the normal tissue; as is evidenced in the sensibility of the newly forming skin which is closing over an open wound, or in the recovery of the sensibility of a piece of "transplanted" skin, which has for a time been rendered insensible by the complete interruption of the continuity of its nerves. The most remarkable example of this reproduction, however, is afforded by the results of M. Brown-Séquard's t experiments upon the gradual restoration of the functional activity of the spinal cord after its complete division; which takes place in a way that indicates rather a reproduction of the whole or the lower part of the cord and of the nerves proceeding from it, than a mere reunion of Spencer there tries, not only to show how new actions may arise in nervous systems and form new reflex arcs therein, but even how nervous tissue may actually be born by the passage of new waves of isomeric transformation through an originally indifferent mass. I can not help thinking that Mr. Spencer's data, under a great appearance of precision, conceal lamentable vagueness and improbability, and even self-contradiction.

* "Mental Physiology," 1874, pp. 339–345.

[See, later, Masius in Van Beneden's and Van Bambeke's "Archives de Biologie," vol. i, Liége, 1880.-W. J.]


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