Page:The American Journal of Psychology Volume 1.djvu/20

 14 LOMBARD :

able couch, so formed as to support the back and head. (See Fig. 2. The right thigh rested in a splint of plaster of Paris, shaped so as to conform to inner and posterior surface, and of such a height as to hold the right knee on a level with the hip joint. The right foot was supported at the same height by a swing suspended by a long cord from the ceiling.

3. The recording apparatus.— (See Plate I, Fig. 2, &.)— The amount of the knee-jerk was revealed in the movement of the foot which it produced, and the extent of this movement was automatically recorded.

A long, light but stiff steel rod extended horizontally backward from the awning on which the foot rested, and at right angles to the lower leg.^ It was fastened to the back of the swing by a ball and socket-joint and it rested, near its free end, in the groove in the circumference of a wheel, which turned so easily as to rotate under the weight of the rod when the latter was pulled forward or pushed backward by the swinging foot.

A steel needle was fastened on the rod at right angles to it, and wrote with its point on a sheet of glazed paper which had been stretched on a board, blackened by the soot of a gas flame, and placed horizontally at a short distance below the horizontal rod. As the foot was jerked forward by the sudden contraction of the quadriceps muscle, following the blow on the ligament, the needle was dragged across the blackened paper and wrote the extent of the movement. As the muscle relaxed again the foot swung back to its original position, i. e., that which was determined by the balancing of the tension of the antagonistic flexors and extensors of the knee.

The under surface of the board on which the paper was stretched was crossed by two parallel grooves, which corresponded to two glass tracks^on the little table on which the board rested. After each experiment the board was made to slide a little to one side, so as to bring a fresh surface of the paper under the needle. The mark made by the needle when the board was thus moved recorded the position of the foot when all was quiet and gave a base line from which to measure the extent of the movements of the foot. At the end of the experiments the records thus obtained were "fixed" by being passed through an alcoholic solution of brown shellac, and the distance moved by the foot as a result of each knee- jerk was measured in mm. and tabulated.

In the experiments in which the effect of respiration on the knee-jerk was studied it was necessary that the record should be made on a moving surface, and therefore the blackened paper was stretched on the drum of a Kymographion.

The Experiments.

Effect of successive bloivs of the same and q different strengths. — The first experiments made with the apparatus described were to determine

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