436 THE POPULAR SCIENCE MONTHLY. 



quo and a muscular, glandular, or other terminus ad quern. 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 over- 

 come. If we call the path itself the " organ," and the rearrangement 

 of the molecules the " function," then it is obviously a case for repeat- 

 ing the celebrated French formula of "X« fonction fait Vorgane." 



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 ? f 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.J 



* Some paths, to be sure, arc banked up by bodies moving through them under too 

 great pressure, and made impervious. These special eases we disregard. 



f We can not say the will, for, though many, perhaps most, human haliits 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 im- 

 pubive 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. Fiskc's " Cosmic Phi- 

 losophy," vol. ii, pp. 142-140, and Spencer's "Principles of Biology," sections 302 and 

 303, and the part entitled " Physical Synthesis " of his " Principles of Psychology." Mr. 



