THE PHENOMENA OF ORGANIC NATURE. 155 



I say that this functional difference is vast, unfathom- 

 able, and truly infinite in its consequences ; and I say 

 at the same time, that it may depend upon structural 

 differences which shall be absolutely inappreciable to 

 us with our present means of investigation. What 

 is this very speech that we are talking about ? I am 

 speaking to you at this moment, but if you were to alter, 

 in the minutest degree, the proportion of the nervous 

 forces now active in the two nerves which supply the 

 muscles of my glottis, I should become suddenly dumb. 

 The voice is produced only so long as the vocal chords 

 are parallel; and these are parallel only so long as 

 certain muscles contract with exact equality ; and that 

 again depends on the equality of action of those two 

 nerves I spoke of. So that a change of the minutest 

 kind in the structure of one of these nerves, or in 

 the structure of the part in which it originates, 

 or of the supply of blood to that part, or of one 

 of the muscles to which it is distributed, might 

 render all of us dumb. But a race of dumb men, 

 deprived of all communication with those who could 

 speak, would be little indeed removed from the brutes. 

 And the moral and intellectual difference between 

 them and ourselves would be practically infinite, 

 though the naturalist should not be able to find a 

 single shadow of even specific structural difference. 



But let me dismiss this question now, and, in conclu- 

 sion, let me say that you may go away with it as 

 my mature conviction, that Mr. Darwin's work is the 

 greatest contribution which has been made to bio- 

 logical science since the publication of the "Regne 

 Animal " of Cuvier, and since that of the " History of 



