96 Mr. Mayo 07i Human Physiology, 



'^ Instinct appears to consist in a natural tendency to 

 the performance of definite voluntary movements upon the 

 occurrence of certain sensations or states of inward feeling. 

 We have experience of its influence in our own persons at 

 every period of life, and can analyze its nature, both under 

 circumstances where it does not admit of controul, and in 

 cases where we are capable of modifying or repressing its 

 impulses.'* 



Having thus defined the simplest elements of a form of 

 consciousness analogous to our own, Mr. Mayo proceeds to 

 show, upon the concurring evidence of comparative anatomy, 

 of experiments made upon animals, and authentic his- 

 tories of acephalous children, that the parts of the human 

 nervous system essentially and exclusively connected with 

 sensation, volition, and the commonest instincts, are the 

 nerves, with the spinal marrow and medulla oblongata. 

 We have not room to extract the testimony upon which the 

 preceding position rests, nor to follow the numerous in- 

 teresting inquiries into which the subject branches. Let us 

 limit ourselves upon this head to a few remarks upon the 

 account of instinct, which Mr. Mayo adopts. 



To consider instinct as a motive actuating the will, not as 

 a principle analogous to volition, and capable of superseding 

 it, has the recommendation of simplicity, and serves better 

 than other hypotheses to explain consistently several re- 

 markable cases. A singing-bird reared from the egg in 

 absolute solitude, or precluded from hearing the song of any 

 other bird, acquires self-taught the note belonging to its 

 kind. On the other hand, a singing-bird brought up ex- 

 clusively with birds of another species, learns the song of 

 that species without acquiring that of its own race. The 

 tendency to imitation is a remarkable characteristic of all 

 animals during the early part of life ; and we seem plausibly 

 and consistently to account for the modification of the instinct 

 here, by stating, that the pleasure attending the imitation of 

 the song of its fellows formed a stronger motive with the bird, 

 than the innate tendency to practise the notes of its kind. 



Animals are led by Instinct to select particular haunts ; 

 if they have been frequently disturbed they desert these 

 haunts, for others naturally less eligible; in this, and si- 

 milar instances, the recollection of the alarm repeatedly 

 experienced, forms a motive for refraining from what the 

 instinct prompts. 



The countenance naturally bears a definite expression for 

 every shade of feeling ; but when most excited, many men 



