on: FIG. 100.--RESPONSES IN SENSITIVE SILVER CELL
Illumination for one minute and obscurity for one minute. Thick line
represents record during illumination, dotted line recovery during
obscurity.]

Another curious phenomenon sometimes observed in the response of retina
is an occasional slight increase of response immediately on the
cessation of light, after which there is the final recovery. An
indication of this is seen in the second and fourth curves in fig. 99.
Curiously enough, this abnormality is also occasionally met with in the
responses of the silver cell, as seen in the first two curves of
fig. 100. Other instances will be given later.

CHAPTER XVIII

INORGANIC RESPONSE--INFLUENCE OF VARIOUS CONDITIONS ON THE RESPONSE TO
STIMULUS OF LIGHT

Effect of temperature--Effect of increasing length of exposure--Relation
between intensity of light and magnitude of
response--After-oscillation--Abnormal effects: (1) preliminary
negative twitch; (2) reversal of response; (3) transient positive
twitch on cessation of light; (4) decline and reversal--Resume.

We shall next proceed to study the effect, on the response of the
sensitive cell, of all those conditions which influence the normal
response of the retina. We shall then briefly inquire whether even the
abnormalities sometimes met with in retinal responses have not their
parallel in the responses given by the inorganic.

[Illustration: FIG. 101.--INFLUENCE OF TEMPERATURE ON RESPONSE
Illumination 20", obscurity 40".
In (_a_) is shown a series of responses at 20 deg. C.--the record exhibits
slight fatigue. (_b_) is the slight irregular response at 50 deg. C.
(_c_) is the record on re-cooling; it exhibits 'staircase'
increase.]

#Effect of temperature.#--It has been found that when the temperature is
raised above a certain point, retinal response shows rapid diminution.
On cooling, however, response reappears, with its original intensity. In
the response given by the sensitive cell, the same peculiarity is
noticed. I give below (fig. 101, _a_) a set of response-curves for
20 deg. C. These responses, after showing slight fatigue, became fairly
constant. On raising the temperature to 50 deg. C. response practically
disappeared (101, _b_). But on cooling to the first temperature again,
it reappeared, with its original if not slightly greater intensity
(fig. 101, _c_). A curious point is that while in record (_a_), before