vi VOLITION IN THE SPINAL CORD 295 



action, and I have done so too, but with a significance not 

 hitherto usual, since I have expressly included in instinct 

 reasoning action inherited through habit. The extent of the 

 idea of instinct is also usually limited within the range of 

 the action of the nervous system by the exclusion of reflex 

 action from it. Only actions or inclinations, i.e. faculties for 

 action, are called instincts which take place as if they were 

 due to reflection without actually being so. 



But there are evidently two kinds of reflex action : one 

 purely involuntary, in the development of which conscious 

 experience, a brain, has had no influence in its earliest phyletic 

 origin. To this kind belongs, for instance, the peristaltic 

 movement of the intestine under the stimulus of food taken 

 into it. Also the rhythmical motion of the heart. To it also 

 belong numerous motions of the parts of lower organisms or 

 of the whole of such organisms excited directly by stimula- 

 tion. In another group of reflex actions, those which were 

 originally voluntary, it is evident that they were once, at an 

 earlier period, under the control of the brain, of experience ; 

 they are really automatic, in all their characters are now 

 removed from all relation to the action of the brain, in such a 

 way that such relation must be deduced from special reflec- 

 tion. Here belong some of those reflexes which take place 

 involuntarily, but which can even now be performed by 

 the will, e.g. the execution of purposeful co-ordinated motions 

 by particular groups of muscles on stimulation of the 

 appropriate nerves. The mechanism at work in this case 

 can only have arisen in consequence of practice originally 

 influenced by the brain, that is, in consequence of experience. 



The reader will be here at once reminded of the well- 

 known experiment with acetic acid upon frogs, which is 

 usually quoted as evidence of the very great importance of 

 reflex action ; when acetic acid is placed upon the skin of a 

 decapitated frog on one side, the nearest limb of that side 



