On the Relation of Muscle Sense to Pressure Sense 3 



strips of oak 600 and 300 mm. in length. 50 mm. wide, and 15 mm. 

 thick. These are set together at right angles to one another, 

 forming a cross. At their intersection a rod, three inches long 

 and drawn down to a point at either end, is passed through the 

 oak strips. This forms the pivot of the balance and is supported 

 at either end by conical depressions in set screws, and these 

 screws rest upon the tops of the two vertical pieces spoken of 

 before. The longer oak strip swings horizontally and the other 

 hangs vertically. The lower end of the later strip swinging be- 

 tween the uprights bears a cork which is brought into contact 

 with the palm when the balance tips in one direction. The scale 

 beam on the opposite side to the cork is graduated to five milli- 

 meter divisions and so adjusted that when a 200-milligram weight 

 is laid upon the outer end it turns easily and decidedly. In oper- 

 ation a lead weight weighing 165 grams was set upon the scale 

 beam at different graduations to give different pressures through 

 the cork upon the palm. This weight was cast with a flat end 

 and a sharp edge so that it might be readily and accurately ad- 

 justed to different graduations. The balance was operated by an 

 eccentric ca:m by which the pressure might be brought upon the 

 palm gradually and as gradually removed. In the experiments 

 the standard weight chosen was the pressure exerted upon the 

 palm when the weight was placed at 150 millimeters from 

 the pivot of the balance. As this was about the same distance 

 as the cork from the pivot the pressure was about equal to 165 

 grams. With care the weight can be readily adjusted to any 

 graduation upon the balance beam within a half millimeter, so that 

 the error arising from this source can not exceed at the outside 

 .3 of one per cent of the standard used in these experiments. 



The experiment began with an attempt to find the threshold 

 for passive pressure upon the palm. Here the hand was firmly 

 clamped in the position described above so as to shut out as far 

 as possible all muscular reactions. It is not possible to prevent 

 all contractions. In fact, when the hand is clamped in whatever 

 manner one soon feels twitchings and tensions begin first in one 

 locality and then in another ; these grow more and more intense 

 until a kind of cramp ensues, which is most painful. Care was 



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