756 Dynamic TJieory. 



ent. It first takes the form of a nervous current clown the efferent 



nerves, and lastly, ends in a stimulation of muscle contraction. 



In tracing the stimulus from the sense organ to the muscle, as above, 

 I have, for the sake of simplicit} r , mentioned it as one stimulus im- 

 pelled from one organ to another. The case is really much more com-: 

 plicated. Before the stimulus reaches us from the outside, it consists 

 of the movement of some sort of matter. If it is a sight stimulus, it 

 is the vibratory movement of the ether in a particular tone. When this 

 reaches the retina it ceases as such vibrations and is succeeded by the 

 motion of a different sort of matter ; viz. , a molecular agitation of the 

 rods and cones of the retina. This agitation communicates motion of 

 another sort to the optic nerve. This motion, which is supposed to be 

 a molecular tremor of the material in the nerve, is rapidly propagated 

 along it from the retina to the brain, and is called a nervous current. 

 In the brain cells with which it connects, the tremor of the nerve is ex- 

 hausted in setting up their molecular agitation which is peculiar to them- 

 selves (a color perhaps), and depends upon their form and molecular 

 constitution and polarity. From cell to cell, through many of the in- 

 ternal sense organs, the motion reverberates, now a current as it pro- 

 gressively thrills the molecules of the connecting nerve fibres, and now 

 setting up polar tension in the cells and re-arranging their molecules. I 

 take it, the action is not precisely the same in any two cells, but each 

 one vibrates in the manner necessarily accompanying its peculiar struc- 

 ture and polarity, and consequently arouses a different sensation of its 

 agitation. Finally, as a result of all these cerebral interactions, an agi- 

 tation reaches and propagates itself along a motor nerve, once more a 

 current. All these organs move in a different manner from the rest, 

 but the motion of each is started by the motion of that next preceding 

 it. We see in this transfer of motion from one body to another in the 

 brain cells, merety an example and illustration of the mechanical trans- 

 fer of energy treated of in chapter 35. Such appearance of energy 

 anywhere must be by transfer. It cannot, without contravention of the 

 law of the conservation of forces, be supposed to come in any other 

 way, and cannot, in the nature of things, be supposed to originate from 

 nothing. 



Maudsley remarks that ' ' a new organism is the product of precedent 

 organisms, and of the external conditions of the medium, but it is neither 

 the precedent organism nor the external conditions ; nor is it merely the 

 arithmetical sum or mechanical compound of them ; it is a new product 

 with properties of its own, distinctly autonomous. " He then applies 

 this conception to the will. He says, "motives are necessary antece- 

 dents of will, but assuredly will is not motive, nor is it simply the sum 

 of the foregoing motives ; it is a new product, the outcome of antecedents 



