CHAPTER XIV 



SENSE OKGANS AND SENSATIONS 



1. The human mechanism a conscious mechanism. Thus 

 far we have repeatedly compared the human mechanism 

 with lifeless mechanisms, and the points of similarity are 

 most interesting and instructive. In the supply of power, 

 the elimination of wastes, the interdependence and coopera- 

 tion of parts, the adjustment to the changing conditions 

 of work, and in many other respects the resemblance holds 

 good. But in one respect there is no likeness whatever. 

 When a human mechanism is not in good working order or 

 is tired, it may be aware of the fact; when an engine is 

 damaged in any way, the engine does not know it. Events 

 taking place in the living animal body arouse in it, and in 

 it only, conscious sensations. 



Sensations are always called forth by the condition of 

 some organ or by the condition of the body as a whole. 

 When several hours have passed since the taking of food, 

 we feel hungry; or of drink, we feel thirsty; when any- 

 thing touches the skin a sensation of touch is aroused; if 

 it presses very hard, that part of the skin feels painful ; if 

 the tongue is acted upon by sugar or salt, we get a sensa- 

 tion of taste ; if light enters the eye, it produces conditions 

 hi that organ which arouse in us sensations of color. In all 

 these cases the conscious sensation is due to the condition of 

 some part of the body. 



2. The reference of sensations. Sometimes we refer the 

 sensation to the part of the body which is first affected, 

 or to the body as a whole, and sometimes we refer it to 



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