324 ZOOLOGICAL PHILOSOPHY 



small rudimentary brain, since it gives rise immediately to the sense 

 of sight. But in the case of animals which have a spinal cord, there 

 can be no doubt that the nucleus of sensations is simple and indivisible ; 

 this nucleus is apparently situated at the anterior extremity of the 

 spinal cord, at the base of what is called the brain and therefore below 

 the hemispheres. 



The sensitive nerves arriving from all parts and terminating in a 

 centre of communication, or in several such nuclei connected together, 

 constitute the harmony of the system of sensations, for they spread 

 throughout the system all the impressions, whether isolated or 

 generalised, that the individual may experience. 



To form a clear conception of the wonderful mechanism of this 

 sensitive system, we must recall what I said before, viz. that an ex- 

 tremely subtle fluid, whose movements of translation or oscillation 

 are nearly as rapid as hght, is contained in the nerves and their nucleus, 

 where it moves freely without escaping. 



If we now consider that harmony which unites all parts of the system 

 of sensations, we see that every impression, internal or external, that 

 any individual receives, immediately causes an agitation throughout 

 the system or the subtle fluid contained in it, and consequently through- 

 out the entire body, although it may pass unperceived. Now this 

 sudden agitation promptly gives rise to a reaction, which is brought 

 back from all parts to the common nucleus, and there sets up a 

 singular effect, in short, an agitation, which is thereafter propagated 

 through the one nerve, that does not react, to the point of the 

 body that was originally affected. 



Man, who possesses the faculty of forming ideas out of what he 

 experiences, has formed one out of this singular effect produced at 

 the nucleus of sensations and propagated to the point affected, and 

 has given it the name of sensation, in the belief that every part 

 that receives an impression possesses in itself the faculty of feeling. 

 FeeUng, however, does not exist anywhere but in the actual idea or 

 perception which constitutes it, since it is not a faculty belonging to 

 any part of our body nor any of our nerves, nor even to the nucleus 

 of sensations, but is purely the result of an emotion of the whole 

 sensitive system which becomes perceptible in some point of our 

 body. Let us examine in further detail the mechanism of this 

 singular effect of the system of sensibihty. 



In the case of animals which have a spinal cord, there start from 

 every part of their body, the most deeply situated as well as the most 

 superficial, nervous threads of extreme fineness, which without any 

 division or anastomosis proceed to the nucleus of sensations. Now 

 these threads, in spite of junctions which they form with others, 



