Chap. XIV. AND SUMMARY. 349 



case of extreme pain, fear, and grief, and they have ulti- 

 mately caused complete exhaustion; they are conse- 

 quently expressed chiefly by negative signs and by pros- 

 tration. Again, there are other emotions, such as that 

 of affection, which do not commonly lead to action of any 

 kind, and consequently are not exhibited by any strongly 

 marked outward signs. Affection indeed, in as far as it 

 is a pleasurable sensation, excites the ordinary signs of 

 pleasure. 



On the other hand, many of the effects due to the 

 excitement of the nervous system seem to be quite in- 

 dependent of the flow of nerve-force along the channels 

 which have been rendered habitual by former exertions 

 of the will. Such effects, which often reveal the state 

 of mind of the person thus affected, cannot at present 

 be explained; for instance, the change of colour in the 

 hair from extreme terror or grief, — the cold sweat and 

 the trembling of the muscles from fear, — the modified 

 secretions of the intestinal canal, — and the failure of 

 certain glands to act. 



Notwithstanding that much remains unintelligible 

 in our present subject, so many expressive movements 

 and actions can be explained to a certain extent through 

 the above three principles, that we may hope hereafter 

 to see all explained by these or by closely analogous 

 principles. 



Actions of all kinds, if regularly accompanying any 

 state of the mind, are at once recognized as expressive. 

 These may consist of movements of any part of the body, 

 as the wagging of a dog's tail, the shrugging of a man's 

 shoulders, the erection of the hair, the exudation of 

 perspiration, the state of the capillary circulation, la- 

 boured breathing, and the use of the vocal or other sound- 

 producing instruments. Even insects express anger, 

 terror, jealousy, and love by their stridulation. With 



