on of the two high points
in figure 9). Although breathing was always deep and regular before and
after a test, during the test it was less deep and irregular. Very often
it was suspended altogether (figures 7, 8 and 9). In ordinary life we
often notice that highly concentrated attention is usually accompanied
by non-voluntary inhibition of movements in the musculature which, for
the moment, is not directly involved; the man lost in thought slackens
his pace and finally stands still, the intent listener or looker-on
holds his breath.

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