364 



NATURE 



[September 14, 191 1 



nervous system. There are, for example, the lens systems 

 of the eyeball rind the sound-conducting and resonant 

 systems of the ear. Now, in dealing with the central 

 nervous system, the suggestion was made that it was 

 developed by just such physical conditions as are trans- 

 mitted through it in its adult form. In dealing with the 

 eyeball, it is clear that an admission of this sort is not 

 easy. During the evolution associated with natural selec- 

 tion the eyeball is formed by light. It must be so. The 

 eye is as perfect an optical instrument as could be made 

 with a full knowledge of the part played by matter and 

 special arrangements of matter in reflecting, refracting, 

 and absorbing light. Long prior to the development of 

 man, who at a later date acquired sufficient knowledge of 

 these properties to aid him in the formation of crude 

 lenses, there was to be found upon the general surface of 

 the animal world lenses of very great perfection, in fact, 

 complete cameras. Had the first optician then known 

 what was in him he would have been saved infinite pains. 

 Had he indeed known even the lens systems formed on the 

 leaves of plants. Surely there is no escape from the state- 

 ment that either external agency cognisant of light, or 

 light itself, has formed and developed to such a state of 

 perfection this purely optical mechanism, and that natural 

 selection can have done no more than assist in this process. 

 The influence of natural selection depends upon the fre- 

 quency of variations, and it is important that there is no 

 variation that has not behind it some cause. In this 

 special case of variation in physical arrangements, it is 

 indeed probable that the most frequent cause of variation 

 would be exerted by physical conditions, since in this case 

 the factors that are thus introduced by variation are not 

 distinguished by any chemical peculiarity. Thinking of the 

 few possible physical causes of variation, there can be little 

 doubt that light itself would produce some change in 

 this optical instrument, and that the variations produced 

 by light would be just those more likely to be adapted to 

 the subsequent traverse of light than such as were acci- 

 dentally produced by some other physical cause. Accepting 

 such a statement, we may say that in the course of 

 development light formed the eye by its action upon such 

 tissues as those of which the general surface of the bodv 

 is composed. Now in just the same way there can be little 

 doubt but that sound formed the sound-conducting and 

 resonant portions of the ear. We may perhaps go further 

 than this statement, and say that ' not only has this 

 mechanism placed in front of the central nervous system 

 been formed in this fashion, but that the parts of the 

 central nervous system behind it have been formed by 

 physical effects transmitted from the ear through this key- 

 hoard where sound is transformed into nervous impulses. 

 Thus also, when thinking of the semicircular canals, repre- 

 senting as they do the portion of the surface of the bodv 

 that is still normally excited by just such changes as 

 affected the whole surface of the animal when its habitat 

 was the sea, there is no need to doubt the view that the 

 structures found there were formed by fluid friction ; and 

 that the cerebellum was formed as a consequence of the 

 stimuli which have been transformed by these surface 

 organs into nervous impulses. 



But if this was the case during the evolution which led 

 up to man, what occurs in the development of the indi- 

 vidual? "We -ran afford to admit the possibility that sound 

 may approach the embryo and that fluid friction is 

 responsible for effects observed, hut light is obviously no 

 factor in this process. Here there is no douht that the 

 eyeball is developed into a very perfect optical instrument 

 in the absence of light, and we must ask : What is the 

 force that in this case imitates the action of light? Some 

 force must be held as arranging the several parts of the 

 eyeball in front of the developing retina, and it is probable 

 that before discovering it we should have to refer to the 

 properties of the retina for an answer. We might indeed 

 say that since the retina is a portion of the central nervous 

 systi in generally characterised by the undoubted possession 

 of electrically charged surfaces, it is always possible that 

 this cause is of an electrical nature. Leave the statement 

 general and it takes the form ili.it the optical mechanisms 

 of the eyeball are formed in the absence of lighl b\ some 

 other definite physical cause or series of causes, Place it 

 temporarily in the form where 1 would like to leave it, 



NO. 2185, VOL - 87] 



both on general grounds and on the evidence that its 

 development is modified by the addition or subtraction of 

 electrolytes : in the absence of light it is probable that 

 orderly electrical forces arrange [he developing parts of the 

 eyeball. Now this is really not a surprising statement, 

 since light may probably, even in the first case, be 

 transformed into some other form of energy such as 

 electrical energy when primarily shaping these surfaces. 

 In any case, however, this is the view, that the individual 

 eyeball is an instrument formed probably by some simple 

 set of physical conditions from which light is absent, 

 and that it is used, after a certain abruptly occurring 

 date, by light, a force that has, up to this time, had no 

 access to it, and yet finds it most beautifully formed for its 

 special use. 



Now development after all is rather a retrograde affair. 

 Consider the fertilised ovum and its possibilities. A physical 

 condition determines an increase in the chemical activity 

 of the nucleus. At the same time an addition is made to 

 the chemical material of the nucleus. The nucleus then 

 divides and forms an ever-increasing site of modified 

 chemical activity. Each new portion of this extending site 

 is surrounded by cell bodies subjected to different sets of 

 physical conditions, and in touch with different qualities 

 and quantities of states. We may take it as certain that 

 not any of the many extraordinary events which take place 

 happen without definite cause. For example, this must 

 be true of every single cell division. Any particular cause 

 bearing similarly on successive generations of cells, or, as 

 we may say, allowed to prolong its action upon a special 

 mass of changing nuclear reaction, must finally produce 

 states of an almost irreversible kind, eliminating possi- 

 bilities of variation. Thus we might describe the ovum as 

 a possible source of countless variations, whereas it is 

 probable the cells of formed tissues are greatly limited in 

 this possibility. Early in these processes, it is true, a 

 portion of still fairly aboriginal material is shut off, and 

 through some cause protected from changes leading to 

 violent modification ; and to this share there still appertains 

 much of the variable character of the original ovum. Part 

 of the remainder, perhaps the whole of the remainder, is 

 under the heavy grip of circumstances which differ widely 

 in different cases, and is step by step slowly driven into 

 something of that deadly monotony of condition which is so 

 evident in the red corpuscle, in the nerve-fibre, and in a 

 somewhat less degree in the nerve-cell. Knowing this, 

 then, we shall only with difficulty be induced to credit any 

 particular kind of subordinate cell with any special 

 character. When, for example, it is stated that the mind 

 is, so far as the evidence will permit the statement, 

 associated with the brain, and with no other part of the 

 central nervous system, we can hardly get behind this 

 statement. Mind, in man, is associated with the brain. 

 It is conceivable that in animals it may be associated with 

 parts of central nervous systems so simple in arrangement 

 that we single out nothing from them as the brain. It is 

 conceivable that there is something of the kind, indeed, in 

 humble uni-cellular organisms. But in man mind is 

 associated with the brain. 



There is also the point that even in the case of the 

 brain, such phenomena as sleep and deep anjesthesia 

 familiarise us with the fact that the mind is not necessarily 

 always associated with the brain, but only with this when 

 in a certain condition. 



Now there is no scientific evidence to support or to rebut 

 the statement that the brain is possibly affected by 

 influences other than those which reach it by the definite 

 paths proceeding from the sense-organs and from the 

 different receptive surfaces of the body. It is still possible 

 that the brain is an instrument traversed freely, as the ear, 

 by sound, by an unknown influence which finds resonance 

 within it. Possible, indeed, that the mind is a complex 

 of such resonances ; music for which the brain is no more 

 than the instrument, individual because the music of a 

 single harp, rational because of the orderly structure of 

 the harp. Consider such a possibility, and the analogy 

 which I have prepared in dealing with the eyeball is seen 

 to have some meaning, inasmuch as an instrument shaped 

 in the embryo by a certain set of conditions may in dis- 

 course of time become the play of some new influence 

 which has taken no immediate part in fashioning it. I 



