Page:The American Journal of Psychology Volume 1.djvu/49

 NORMAL KNEE-JERK. 43

ference of one mm. between the averages of the two examinations, and that on three days, the 1st, 2d and 7th, the average was considerably greater before than after lunch. With regard to the effect of dinner, one observes that the average was greater after than before dinner on nine of the twelve days on which both examinations were made, that it was only two mm. greater before than after dinner on one of the remaining days, the 11th, and that it was 5 mm. and 6 mm. greater before than after dinner on, respectively, the 1st and the 4th.

As everyone knows, the result of a hearty meal is to make one feel quiet and indisposed to work, while the effect of a moderate meal is to rest and invig- orate. If one has been working hard up to the moment of meal time, the tire is at first unnoticed, because the excitement still remains, and it is only after an interval of quiet that one becomes con- scious of the weariness. Inasmuch as the activity of the mind has a great influence upon the extent of the knee-jerk, as will be shown hereafter, it is probable that the mental condition is in a great degree responsible for the exceptions which have been noted. An examination of the averages de- rived from all the experiments taken during the two weeks, before and after the three meals, is to be found at the bottom of the table, and it shows that the knee-jerk was, on the average, always greater after, than before, each of the three meals. It may be justly stated, therefore, that the effect of a meal is to increase the knee-jerk, but that this tendency is not so strong but that it is frequently overcome by counteracting influences.

It may be well to note here that no wine or beer