THE PRESSURE-SENSE. 



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suddenly than when gradually increased. Decrease of pressure is less 

 readily perceived than increase. 



2. Intermittent variations of pressure are more readily recognized 

 than light pressure, rapid variations with more difficulty than those 

 occurring at longer intervals. 



The greater the sensitiveness of a portion of the skin the more rapidly may 

 individual impulses or blows follow one another and yet be perceived as separate: 

 on the posterior aspect of the thigh 52, on the back of the hand 61, on the finger- 

 tips 70 impulses in a second. 



3. Differences between two weights are perceived by the finger- 

 tips when they are in the ratio of 29:30 (by the forearm when the ratio 

 is 18.2 : 20), provided that the weights are not too light or too heavy. 



FIG. 342. Landois' Mercurial Pressure-balance. 



Ascending from light to heavier weights, the accuracy in distinguishing 

 between two weights increases at first, and then decreases rapidly for 

 heavier weights. This observation is contradictory of the psycho- 

 physical law of Fechner. 



4. A. Eulenburg found the following gradations in the accuracy of 

 the pressure-sense: the forehead, the lips, the back of the tongue, the 

 cheek, and the temple showed differences of from -$ to -^\ (from 200 : 205 

 to 300:310 gm.). The dorsal aspect of the last phalanx of the 

 fingers, of the forearm, of the hand, of the first and second phalanges, 

 the palmar aspect of the hand, and of the forearm and the arm perceived 

 59 



