Of the three curves registering the movements of the head, we find that nothing peculiarly characteristic is revealed by the two upper ones, giving the movements up and down, and to the right and left, respectively. They are the ordinary tremor-like movements and indicate nothing beyond the fact that the subject is unable to hold his head absolutely quiet for even one second. It is the third line that is of interest to us, for it is here that the oft-mentioned head-jerk (which indicates arrival--in the counting--at the number expected) registers itself. The moment of the head-jerk corresponds, almost without exception, with the moment of the first deep inhalation,--just as one would be led to expect from common experience. But we are not to regard the head-jerk as a result of the inhalation, for it also occurs when the subject complies with the request that he hold his breath during the test. The actual height of the jerks recorded in figures 6 to 12 was 1/4 to 1-1/2 millimeters and the average height obtained from the forty curves of these four subjects was 1 millimeter. There is great individual variation: the greatest height that was obtained from the records was 2-3/10 millimeters, the lowest 1/10 millimeter. The variations within the records of the several individuals are comparatively slight and are evidently dependent, in the main, upon the degree of concentration of attention. Thus in the case of von Allesch, where in 75 tests the average height of the jerk is 1 millimeter, the mean variation is 4/10 millimeter. If, in order to obtain some idea of the size of Mr. von Osten's movements,[S] we compared the values gained in the laboratory with those which would probably obtain in his case, we would say that his head movements were more minute than almost any of those of which we obtained records. At the most they could not have been more than 1/5 millimeter (when measured in terms of the distance through which the brim of his broad hat moved, they would appear to be about 1-1/2 times as large. See page 49.) The movements of Mr. Schillings, on the other hand, were certainly four or five times as great as those of Mr. von Osten, and occasionally even greater than that. When we turn to consider the time-interval elapsing between the subject's final head-jerk and my reaction (as recorded in the sixth curve), we find that the reaction-time averages 3/10 seconds, a value which agrees very favorably with that estimated for the horse (page 56). Thus it appears that man and beast have the same reaction-time--though we must bear in mind that I worked under some difficulty, since I had to care for the apparatus.