94 ORGANIC EVOLUTION — THE FACTORS 



Mr. Silencer next discusses a question with which we 



football team, had his left forearm broken in a hotly-contested 

 game, wliile playing his eleven against that of another institution. 

 Tlie surgeon who was called did his work in such a bungling 

 manner tliat after the bones had begun to knit, the arm had to be 

 broken over again in order to set it j)roperly. To keep it in the 

 correct position a plaster cast was made whicli held it firmly. 

 This plaster-of-paris case extended from tlie knuckles to a point 

 above the ell>ow. After three months the case and bandage were 

 removed. Of course, during the entire jDcriod when encased in 

 the plaster, the forearm had not been moved either at the wrist or 

 at the ell low, I then endeavoured to test tlie sensibility of the 

 skin on this arm whicli had not been moved for so long a time. 

 To do this I applied the points of a pair of dividers or compasses 

 which were separated more or less Avidely, after the manner of the 

 usual iosthesiomctric tests. The i'orearm was divided into four 

 dift'erent areas for the purposes of more accurate comparison with 

 the sensitiveness of the skin on the uninjured right forearm of the 

 same person. Without going into detail, it should be stated that 

 on the left forearm — the one so long immovable — when the two 

 points touching the skin at a given locality were separated by as 

 much as 55 millimeters, they were felt as one instead of two ; while 

 on the right forearm they would only have to be about 20 milli- 

 meters apart in order to be perceived as two. On the back of the 

 ' lame ' arm, at a dilferent locality from that just mentioned, it 

 was found that even when the two points of the dividers were 75 

 and 80 millimeters apart, they were felt as one ; while at a 

 corresponding locality on the right arm the skin was so sensitive 

 that points but 17 millimeters apart could be felt as two. It must 

 also be observed that this particular person, with reference to a 

 large number of activities, had always previously been practically 

 ambidextrous — indeed, he never had to favour the left arm at all. 

 In his position as gymnasium instructor, he could (before the 

 accident) manipulate the dumb-bells, Indian clubs, play base-ball, 

 hand-ball, and the like, with the left hand as well as the right. 

 It would seem, then, that the sensibility of the skin over the 

 injured forearm was lost simply because that member was for so 

 long a time immovable. This has an important bearing on the 

 oft-mentioned principle, to the effect that " the localizing power 

 is delicate in proportion as the skin covers a movable part of 

 the body."— Professor W. O. Krohn, Psychological Eevieut, pp. 

 280-1. 



It will be observed that Professor Krohn attributes the decrease 

 of sensitivity to the lack of movement, but I think it cannot be 

 doubted, that it should rather be attributed to the lack of appro- 

 priate stimulation, to the fact that for a length of time tactual im- 

 pressions were not received by the skin of the encased arm, in 

 consequence of which variations acijuired during the lifetime of 

 the individual were lapsed in part or whole. 



