PRESIDENTIAL ADDRESS. 531 



of the semicircular canals, representing as they do the portion of the surface of 

 the body 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 individual? We can afford to admit the possi- 

 bility that sound may approach the embryo and that fluid friction is responsible 

 for effects observed, but light is obviously no factor in this process. Here there 

 is no doubt 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 system 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 that the optical mechanisms 

 of the eyeball are formed in the absence of light by some other definite physical 

 cause or series of causes. Place it temporarily in the form where I would like 

 to leave it, 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 the developing parts of the 

 eyeball. Now this is really not a surprising statement, since light may pro- 

 bably, 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, how- 

 ever, this is the view, that the individual eyeball is an instrument formed pro- 

 bably 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. A tthe 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 possibilities 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 modifica- 

 tion ; 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 widelv 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 

 soecial 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 state- 

 ment. 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 also 



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