36 LOMBARD :
Common experience teaches that when one is well, there are three principal influences which lower the activity of the body : fatigue, hunger and depressing weather ; while rest, a meal and invigorating weather increase the activity. One has also learned that even when the general condition is depressed by these influences it may be temporarily roused by any cause of mental excitement, and that when it is in a vigorous state it may be temporarily lowered by drowsiness.
Substitute in the above statements knee-jerk for activity of the body, and they will be equally true. These facts were illustrated in our experiments by a diurnal decline of the knee-jerk, interrupted at meal time, and varied by changes in the weather, fatigue, and by causes of mental excitement.
Explanation of the chart, Fig. 3, ivhich shows all
the variations of the knee-jerk which occurred in the
course of one day of this series of experiments. —
Before studying the results of the experiments as
a whole, the writer wishes to illustrate still more
clearly the great number of variations to which the
knee-jerk is subject in the course of a single day.
The following chart shows the extent of the movement of the foot in millimetres in each experiment taken in the course of one day. All the experiments made at the time of one examination are grouped together under the figures which show the time at which the examination was made. Each dot represents a separate knee-jerk, and the connecting lines are given to enable the eye to more readily grasp the extent of the variations. The heavy hori- zontal lines show the average of all the experiments through which they are drawn. At the top of the table is given roughly the day's journal, and in the body of the table are remarks accounting for reinforcements, the causes of which were thought to have been recognized.
