slight, then more pronounced, and lastly shows a tendency to approach a
limit. In all this we have a perfect parallel to corresponding phenomena
in animal and vegetable response. We saw that the proper investigation
of this subject was much complicated, in the case of animal and
vegetable tissues, by the appearance of fatigue. The comparatively
indefatigable nature of tin causes it to offer great advantages in the
pursuit of this inquiry. I give below two series of records made with
tin. The first record, fig. 83, is for increasing amplitudes from 5 deg. to
40 deg. by steps of 5 deg.. The stimuli are imparted at intervals of one minute.
It will be noticed that whereas the recovery is complete in one minute
when the stimulus is moderate, it is not quite complete when the
stimulus is stronger. The recovery from the effect of stronger stimulus
is more prolonged. Owing to want of complete recovery, the base line is
tilted slightly upward. This slight displacement of the zero line does
not materially affect the result, provided the shifting is slight.

[Illustration: FIG. 83.--RECORDS OF RESPONSES IN TIN WITH INCREASING
STIMULI, AMPLITUDES OF VIBRATION FROM 5 deg. TO 40 deg.
The vertical line to the right represents .1 volt.]

TABLE SHOWING THE INCREASING ELECTRIC RESPONSE DUE TO INCREASING
AMPLITUDE OF VIBRATION

+---------------------+----------------+
| Vibration amplitude | E.M. variation |
+---------------------+----------------+
| 5 deg. | .024 volt |
| 10 deg. | .057 " |
| 20 deg. | .111 " |
| 25 deg. | .143 " |
| 30 deg. | .170 " |
| 35 deg. | .187 " |
| 40 deg. | .204 " |
+---------------------+----------------+

The next figure (fig. 84) gives record of responses through a wider
range. For accurate quantitative measurements it is preferable to wait
till the recovery is complete. We may accomplish this within the limited
space of the recording photographic plate by making the record for one
minute; during the rest of recovery, the clockwork moving the plate is
stopped and the galvanometer spot of light is cut off. Thus the next
record starts from a point of completed recovery, which will be noticed
as a bright spot at the beginning of each curve. With stimulation of
high intensity, a tendency will be noticed for the