316 ZOOLOGICAL PHILOSOPHY 



by M. Richerand in his Physiologie (vol. li., p. 144 et seq.). " This 

 hypothesis," he says, " is so absurd that there is reason for astonish- 

 ment at the favour that it has long enjoyed." 



The same thing might well be said of the hypothesis of vibration 

 among molecules so soft and inelastic as those of the medullary sub- 

 stance of nerves, if anyone were to suggest it. 



" It is much more reasonable," M. Richerand continues, " to believe 

 that the nerves act by means of a subtle, invisible, impalpable fluid 

 to which the ancients gave the name of animal s'pirits." 



Farther on, when examining the special properties of the nervous 

 fluid, this physiologist adds : " Have not these conjectures acquired 

 some degree of probability, since the analogy between galvanism and 

 electricity, originally suggested by their discoverer, has been confirmed 

 by those remarkable experiments of Volta, which are at this moment 

 being repeated, discussed and expounded by all the physicists in 

 Europe ? " 



However manifest may be the existence of the subtle fluid by means 

 of which the nerves work, there will be for a long time and perhaps 

 for ever, men who dispute it because it cannot be proved except by 

 effects which could not be produced in any other way. 



Yet it seems to me that when all its effects unite to demonstrate 

 its existence, it is wholly unreasonable to deny it on the mere grounds 

 that we cannot see the fluids. It is particularly unreasonable to do so, 

 seeing that we know that all organic phenomena result exclusively 

 from relations between moving fluids and the organs concerned. It 

 is still more unreasonable when we remember that the visible fluids 

 (blood, lymph, etc.) which travel to the nerves and brain and penetrate 

 their substance are too gross and move too slowly to be capable of 

 giving rise to actions of such swiftness as those involved in muscular 

 movement, feeling, ideas, thought, etc. 



As a result of these reflections, I recognised that in every animal 

 which possesses a nervous system there exists in the nerves and in the 

 medullary nuclei where the nerves terminate, a very subtle, invisible, 

 containable fluid, that is but little known since there are no means for 

 examining it directly. This fluid, which I call nervous fluid, moves 

 with extraordinary rapidity in the substance of the brain and nerves, 

 and yet does not form any visible channels in them for the transmission 

 of its movements. 



It is by means of this subtle fluid that the nerves work, that muscular 

 movement is set going, that feeling is produced, and that the cerebral 

 hemispheres carry out those acts of intelligence to which they give 

 rise in proportion to their development. 



Although the actual nature of the nervous fluid is little known to us 



