Franz, Scnsatiojjs foUmvnig JSlerve Division. Ill 



wliicli are not calloused."^ On the lips and parts of the face, a wisp 

 of cotton wool weighing 20 mg. and bending at 200 to 250 mg., was 

 just sufficient to produce a sensation. At times it is more convenient 

 to use a camel's-hair brush, although Head has objected to the use 

 of this instrument. I find it to be a more constant stimulus, in that 

 it remains the same in bending strength for long periods. With 

 cotton wool it is difficult, if not impossible, to select for each day's 

 series of experiments an amount equal to that used on previous 

 days, and if the same piece be used on successive days, it soon loses 

 its original strength. In the experimental results that follow, I 

 have used both cotton wool and a camel's-hair brush. I selected a 

 long haired brush from which I cut off most of the outside hairs, 

 leaving a brush 24 mm. long from the end of the hairs to the inser- 

 tion, with about 125 hairs. As thus modified, the bending strength 

 of the brush was 100 mg. for very slight bending, and about 200 mg. 

 for more extensive bending. These figures are to be compared with 

 the bending strength of the wisps of cotton wool mentioned above. 

 I have found that the same results follow the use of the brush as 

 the use of the cotton wool, and since, as mentioned above, it is more 

 constant, it can be used for many patients as well as the same 

 patient at different times. 



For further tests I have employed the touch instrument of Bloch, 

 which is illustrated in the accompanying figure. To a piece of wood 

 was attached a spring steel wire A which was bent at a right angle 

 B ; the long part of this wire A measured six inches. The area of 

 cross section was about 0.1 square mm. A scale E attached to the 

 instrument enabled the experimenter to determine the pressure made 

 by the wire in bending. The right-angled "piece of wire was pressed 

 against the subject's skin, care being taken to keep it vertical all 

 the time, and when the patient reported that the pressure was per- 

 ceived, the reading was taken from the scale and recorded. Two 

 instruments of this character were constructed, one of which was 



*IIead and Sherren do not give any figures regarding tliese matters. In 

 some later vvorlv, Head used a series of von Frey hairs with bending pressures 

 of 830, 3G0, 230 and 100 mg., respectively. Tlie use of tliese, however, more 

 nearly apjiroaches the use of the esthesiometer which will he described later. 



