370 



THE SENSES 

 FIG. 222 



Diagrammatic cross-section through the ampulla of a semicircular canal: AM, ampulla; CR, 

 acousticf crest; CB, basal cells; CS, support-cells; cc, cuticle; ca, acoustic (noise?) cells and 

 their hair-like projections; 'N, nerve-fiber of the sound-cells. (Duval.) 



FATIGUE, THIRST, AND HUNGER. 



Fatigue, thirst, and hunger may well be classed together as the most 

 important of the general sensations. They each have an unpleasant 

 tone and well illustrate how complex the sensations may be. They 

 arise in the tissues of the body generally, without being sensations in the 

 physiological sense of possessing end-organs, nerves, and cerebral centers. 

 Fatigue, thirst, and hunger, then, are on the border-line between physio- 

 logical sensations as so defined and the host of psychophysiological 

 feelings. 



Fatigue in its origin is chiefly either muscular or neural: our "bodies" 

 may be tired or our "brains," or both. A hard day at trouting in some 

 mountain river of the wilderness is apt to give in its purity the sense- 

 feeling of muscular fatigue ; ten hours' work on the books of a bank 

 afford an excellent idea of what is meant by neural fatigue ; while a day 

 on foot at a world's fair would combine these two in a particularly tiring 

 way, each sort lending elements of intensity to the other. 



In discussing briefly the bodily aspect of the feeling of fatigue, one 

 must discriminate it in the first place sharply from exhaustion. One is 

 physiological, the other pathological. The former may be recovered from 

 within the ordinary periods of rest, but the latter is a matter of incapacity 

 for days in the case of muscles or for many months at times (neuras- 

 thenia) when the central nervous system is involved. It is likely too 

 that in muscular fatigue actual tearing of nerve-fibrils has taken place, 

 for it is quite abolished by what we know as training (Hough, Wood- 

 worth). By this means the organs of the motor apparatus, muscular, 



