ZOOLOGY. 853 



cal action on the nerves, -which gives rise to the phenomena of taste 

 and srnell. All chemical action, however, arises, as far as it can yet 

 be ascertained, from certain relative movements in the ultimate 

 atoms of bodies, and it is these movements, which, in the case of taste 

 and smell, really give rise to the peculiar sensations so designated. 

 One striking proof of this is, that the similar atomic action can be 

 produced by magnetism, and that various tastes, particularly that of 

 phosphorus, can be produced by the introduction of magnetic plates 

 into the mouth ; thus most obviously proving that the phenomena of 

 taste are really produced, like those of heat, by the motion of certain 

 minute particles, whether of some magnetic fluid, or of anything else, 

 when subjected to chemical action. By these atomic movements the 

 nerves are affected, just as they are affected by the infinitesimal 

 oscillations of light and heat ; so that the same law holds good through- 

 out, and thus enables us to connect the phenomena of sensation uni- 

 versally with motion as its immediate external antecedent and excit- 



ing cause. 



Looking now from the physical side of sensation to the mental, we 

 shall find that the view we have just taken solves or dissipates many 

 of the difficulties in which the question has always seemed to be in- 

 volved. First of all, it makes the external cause and the effect upon 

 the nervous system quite homogeneous. Outward motion is the 

 cause, inward motion is the effect. Instead of having the solid 

 forms of the outward world standing as it were face to face with the 

 nervous energy, and being obliged to consider how it is possible for 

 two things so entirely heterogeneous to come into so close a state of 

 mental action and reaction, we have now the whole problem reduced 

 to two developments of motion : first, motion in the fluids around us ; 

 and, secondly, a certain determination given, by their means, to the 

 atomic movements or vibrations of the nerves. How the movements 

 of the nerve-force are converted into those of mind-force, we cannot 

 say, any more than we can explain how it is that mechanical motion 

 is converted into heat, or vice versa ; but the outward phenomena 

 are traced, in the way we have now indicated, as far back to the in- 

 ward consciousness as seems possible, without breaking through the 

 last film of separation that divides the conscious from the unconscious 

 world. 



Secondly. The theory we have adopted enables us to draw a clear 

 line of separation between sensation (properly so called) and all the 

 subsequent mental phenomena which attach themselves to it. Thus, 

 taking the sense of hearing, we can now easily strip away every pos- 

 sible association which connects itself with what we hear, and under- 

 stand that the sensation of hearing itself simply implies the nervous 

 effect of certain atmospheric vibrations, and nothing more. Taking 

 the sense of sight, we can at once negative the possibility of sensizing 

 size, shape, thickness, distance, or any other of the properties of 

 bodies ; all we see sensationally is color, as being the direct result in 

 the consciousness of the luminous vibrations which affect the optic 

 nerve. And so, in like manner, does every sense confine itself to 

 one single and peculiar series of phenomena, which are not by any 

 means to be confounded with the mental acts and associations after- 

 wards connected with them. 

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