234 PHYSICAL EXPEESSICXN". 



I explained what is here meant by the term im- 

 pressionability, and it was shown to be a property 

 possessed by inorganic bodies as well as living 

 beings ; and impressionability of the brain is 

 dwelt upon in the chapter on "Expression of the 

 Mind." This is a very large subject, and there are 

 many kinds of impressionability, such as to the 

 effects of light, sound, etc. 



A curious form of impressionability is the ready 

 susceptibility to the formation or building up 

 (trophic action) of new reflexes. A picture when 

 first seen attracts the attention but little ; the head 

 and eyes do not with certainty and quickness turn 

 towards the picture when it comes within the field 

 of vision, but after a time the picture makes an 

 impression upon the nerve-centres by the light it 

 reflects, and the head and eyes then always turn 

 towards it when it is in view. It is more difficult 

 to understand how a series of movements spreading 

 over some considerable period of time can follow 

 from a single short impression. When the brain 

 readily retains impressions it is said to be retentive, 

 and retentiveness in the brain is very important to 

 intellectuality. 



The emotions are usually considered as the out- 

 come of the mind, and before considering any of 

 the expressions of mind it is convenient to consider 

 what can be said about the expression of instinct. 



Instinct is defined by Professor Bain * as un- 

 taught ability. " It is the name given to what can 

 be done prior to experience or education ; as suck- 



* " Mental and Moral Science," 1872, p. 68, 



