Mr. Spencer next discusses a question with which we
football team, had his left forearm broken in a hotly-contested game, while playing his eleven against that of another institution. The surgeon who was called did his work in such a bungling manner that after the bones had begun to knit, the arm had to be broken over again in order to set it properly. To keep it in the correct position a plaster cast was made which held it firmly. This plaster-of-paris case extended from the knuckles to a point above the elbow. After three months the case and bandage were removed. Of course, during the entire period when encased in the plaster, the forearm had not been moved either at the wrist or at the elbow. I then endeavoured to test the sensibility of the skin on this arm which 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 widely, after the manner of the usual æsthesiometric tests. The forearm was divided into four different 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 millimeters apart in order to be perceived as two. On the back of the 'lame' arm, at a different 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 Review, 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 appropriate stimulation, to the fact that for a length of time tactual impressions were not received by the skin of the encased arm, in consequence of which variations acquired during the lifetime of the individual were lapsed in part or whole.
