Abstract
In this investigation the extent of the knee-jerk is compared with the extent of the Achilles-jerk. Apparatus has been devised which is capable of automatically delivering stimuli of uniform intensity, at a constant rate, to both the ligamentum patellae and the tendon Achilles.
In case of the knee-jerk, the subjects were seated in an adjustable chair so that they could be placed in proper proximity to the stimulating hammer. The leg was attached to a movable stylus, suspended from a rubber band, which records the lateral movement on a revolving drum. In all cases a constant leverage was maintained by keeping the point of attachment to the leg at a uniform distance of 30 cm. from the inferior margin of the ligamentum patellae. The details of the technique may be found elsewhere. 1
For the Achilles-jerk experiments, the subjects were placed in a prone position on a well padded table, equipped so that the leg in question could not move. The apparatus is so devised that a stimulating hammer falls upon the tendon Achilles ten times per minute with a force of 296 grams. The extent of the movement of the toe is recorded by connecting it to a moveable stylus, as previously described. A constant leverage was maintained by keeping the point of attachment of the toe 26 cm. from the malleolus medialis.
The extent of the jerks was obtained by measuring the distance in millimeters tbrough which the stylus moved when they were elicited. This distance is referred to as the “extent” or “height” of the jerk.
In this investigation 115 normal subjects were used. The data obtained from 95 subjects are shown in condensed form in Table I. In the case of 20 subjects either one or both jerks was absent, and thus these data are treated separately.
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