Page:The American Journal of Psychology Volume 1.djvu/50

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LOMBARD :

was used with the meals, but that coffee was taken with breakfast and dinner, and tea with lunch.

Effect of Muscular Fatigue upon the Knee- Jerk. — As has been shown, the knee-jerk, by its diurnal variations, illustrates the gradual loss of vigor which the body, as a whole, suffers from morn- ing till bed time, and the temporary and partial re- coveries which it undergoes, as a result of the fresh supplies of nutriment and of rest which it obtains at each meal.

The phenomenon is still more markedly affected by the voluntary exercise of the muscles which are directly concerned in its production. A proof of this statement is offered in the experiments recorded in the following table :

Time of Exam. Extracts from Journal. Average Knee- Jerk.

11 A. M. .After writing half hour 71 mm.

11.15 A. M. .After walking up and down stairs 15 min. .28 mm.

11.45 A. M. .After talking earnestly 32 mm.

1 P. M. .After studying curves an hour 44 mm.

2.15 P. M. .Just after lunch 46 mm.

Here one sees that the effect of walking up and down stairs for fifteen minutes was to decrease the average extent of the knee-jerk from 71 mm. to 28 mm. There can be no doubt but that the change was the result of the exercise, for during the next two hours of quiet the average gradually increased, in spite of the fact that hunger and general fatigue must have tended to lower it. Numerous illustra- tions of the decrease of the knee-jerk, as a result of the voluntary exercise of the muscles of the leg, have occurred in the course of our experiments ; thus, we have always found that the phenomenon was markedly decreased by a walk or even a short stroll. This observation is of importance to the