36 INTRODUCTION. 



cent undisturbed condition, before its action can be 

 [farther] continued or repeated *. 



The alimentary transmutations necessary to vege- 

 tative life are operated through the medium of irri- 

 tation ; thus the food irritates the intestinal canal, 

 the blood irritates the heart, fyc. These movements 

 are all independent of volition, and indeed of con- 

 sciousness,^; least during the continuance of health ; 

 the nerves which produce them are differently ar- 

 ranged in many parts from those which are appro- 

 priated to sensation, or subservient to the action of 

 the will; and the precise object of this different 

 arrangement appears to be to withdraw them from 

 any such connexion. 



The nervous functions, which are sensibility and 

 muscular irritability |, are always performed with 



* It must be recollected that the opinion of Cuvier respecting 

 the existence of a nervous fluid is merely a physiological inference, 

 in support of which we have no direct proof. Nor, indeed, have 

 we any more satisfactory evidence to adduce in opposition to its 

 existence, than that such a fluid is not demonstrable to the senses. 

 Granting, however, this doctrine to be correct, it requires the in- 

 troduction of the words included within brackets to make the 

 explanation accord with the phenomena to which it refers. We 

 think the opinion in question evidently shews that Cuvier has been 

 insensibly betrayed, by the fashion prevailing in physiology at the 

 time in which the above was written, to ascribe too much, and to 

 resort too frequently, to chemical phenomena, in explaining the 

 changes and operations which take place in, and which charac- 

 terize, a living animal. 



t With respect to the source of irritability, physiologists still 

 continue to differ — some ascribing it to the nervous functions, 

 others considering it a property of the muscular fibre, inde- 

 pendent of the nervous influence. The Annotator agrees with 



