NORMAL KNEE-JERK. 61
the week, he was able to forget the blows of the hammer and to think only of the music.
Reinforcements Produced by Exciting Dreams. The fact that the amount of the knee jerk is largely dependent on the activity of the cerebral centers, which are the seat of the emotions, has received another and curious illustration in the course of our experiments. As has been said, the subject, when tired, not infrequently dozed off toward the end of an examination, or, at least, so far lost consciousness that he became no longer responsible for his thoughts. Thus, it not infrequently happened that he pictured himself as kicking a football, or straining to lift a heavy weight, or steadying himself to aim a pistol, or as performing some other vigorous action, and if, as was not seldom the case, the blow on the ligamen- tum patellae was struck at such a moment, he was recalled to himself by the unusual violence of the re- sulting knee-jerk. This was not a single experience, but happened many times, so that the subject had no doubt of the correctness of the observation.
Even during sleep, then, cerebral activity is mak- ing itself felt throughout the body. This fact scarcely needed a proof, for every one has noticed the running movements of sleeping dogs, etc. It is interesting in this connection, however, because evidence thus obtained is much more trustworthy than any which could be gained during waking hours, when the sub- ject might be thought unintentionally to help to bring about the results.
Influence of the Weather Upon the Knee- Jerk. — In the course of the experiments the subject noticed that his general condition and his knee-jerk were be-
