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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



consecutively. Every outward impression is the 

 beginning of a series of nervous acts, following 

 each other from place to place in the nervous 

 system, like the leaps of a waterfall, incessantly 

 modified and linked together in a special order. 

 This is very plain as to the spinal cord, in which 

 physiologists have succeeded in detecting in this 

 way as many as three successive stages of ner- 

 vous action going through three transformations. 



The nerves of the body do not ascend to the 

 brain, as Descartes supposed. Outward impres- 

 sions, then, are not all directly transmitted to the 

 very seat of intelligence. The nerves end at the 

 spinal cord, in a mass of gray matter, which in 

 turn is connected by other tubes with the brain. 

 In this gray matter impressions from without un- 

 dergo a first transformation ; they become what 

 physiologists at the present day call unconscious 

 sensations. This may very readily be established 

 by experiments ; but observations made on the 

 bodies of beheaded persons are still more decisive. 

 In a trunk so mutilated, those perceptions which 

 have their seat only in the head are of course de- 

 stroyed. Now, if the arm hanging down on the 

 table is pricked, it moves away briskly. This 

 movement, more or less irregular, originates from 

 an unconscious sensation awakened in the spinal 

 cord ; it is this unconscious sensation which, trans- 

 mitted to the brain in the living man, becomes 

 there, by a new transformation, a conscious per- 

 ception. It does not seem that any outward 

 impression made on our organs can at once be 

 perceived, without having first, in preparation, 

 undergone one or several of those transforma- 

 tions which are no longer a matter of question 

 as regards the nerves of the trunk, and which 

 are proved by anatomy to exist also as regards 

 those senses, such as the eye and the ear, which 

 are, or at least seem to be, connected in a more 

 direct way with the brain. 



This unconscious sensation of the spinal cord, 

 which is thus transmitted to the head, where it 

 becomes perception, is at the same time commu- 

 nicated in another way to the cord itself, and 

 there transformed to that motive excitement which 

 gave rise to the movement of the arm in the dead 

 body. The fact is, that every mass of gray mat- 

 ter, every centre of transformation, is connected 

 on all sides with an infinity of other centres, with 

 which it is in more or less active communication, 

 and which it influences more or less. The nervous 

 system in its entirety may be likened to a huge 

 telegraphic network. Dispatches from the fron- 

 tier to the capital are transmitted by the shortest 

 way ; but from each of the intermediate stations 



they may be sent in different directions, and may 

 even return toward the starting-point. Only the 

 comparison is incomplete, for we conceive that the 

 telegram will continue unchanged in its course, 

 while the efflux sent along the conductors of the 

 white matter, and received by the gray matter, is 

 modified, transformed, changed in nature in some 

 sort, at every station that it passes. If we imagine 

 the telegraphic network of our illustration placed 

 wholly under a single authority which guides it 

 and directs its mechanism according to his will, 

 it will be able, in spite of its extreme complexity, 

 to work with admirable unity, each dispatch reach- 

 ing its destination by the proper route, without 

 losing itself on the way, going astray, or passing 

 beyond the right point. But things do not go on 

 thus in the nervous system. Partly subject to 

 us, it is also in part freely exposed to all the in- 

 fluences of the outer world. If we admit that 

 the will, a kind of central power, directs when, 

 and as it chooses, the orders it sends to remote 

 organs, these organs, subject to all dangers, ex- 

 posed to the most diverse circumstances, hurt or 

 soothed at the most unforeseen moments, send 

 out every instant the news of these impressions 

 toward the inmost sense, the common centre, and 

 these impressions, setting out from one point or 

 another, trouble the network with some kind of 

 agitation, and even give a shock to the whole of 

 it when they are too violent. 



To this first cause of disorder which depends 

 on the medium which our nature comes in con- 

 tact with, another of an interior kind is added, 

 in the state of deterioration or wearing out of the 

 instruments of health or disease, in the influence 

 of some substances, as coffee, which seem to stimu- 

 late the functions of the brain, or others which 

 clog them, all these being causes which in turn 

 influence the transmission and transformation of 

 nervous action. The struggle between all these 

 so differing influences was known and studied 

 long before there was any suspicion of the ex- 

 planation we now give of it, knowing as we do 

 the course followed in many cases by these mani- 

 fold currents that oppose or combat each other. 

 The time taken by an outward impression to reach 

 our inner sense depends much on the attention, 

 which in a manner suppresses all those neighbor- 

 ing currents that might thwart the one we are 

 awaiting, or disturb its effect. When the way is 

 thus clear, the length of time between an impres- 

 sion on the senses and its perception is almost 

 inappreciable ; but it seems then that impressions 

 other than the expected ones must follow a lon- 

 ger course, or at least are retarded in their prog- 



