14 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY, 
previously negative organisms, these are now nearly all posztive to this 
intensity of light. Next morning (11 a.m.) both sets of organisms, which 
had remained in the dark room overnight, when tested by candle light 
were strongly positive. They were at once taken out of the dark-room 
and placed on the window bench in the north room in fairly strong diffuse 
daylight (it had been snowing, and the hill across the Bay from the 
Station was covered with snow). All the organisms in the originally 
negative plate were now negative again; those in the originally positive 
plate were mixed about three-fourths negative and the remainder positive. 
The two plates were once more carried back to the dark room and 
tested to candle light. The originally negative plate, which a few 
minutes before had been completely positive in the dark room to candle 
light, had now, on account of its short sojourn in the diffuse daylight, 
turned to partially negative and partially positive in about equal groups. 
The originally positive group was still all positive to the candle light, 
although a few minutes previously in the diffuse hght of the window 
about three-fourths of the organisms had been positive. 
Three points are shown clearly in this experiment. 
First, that the reaction varies in the same organism at the same time 
with the intensity of the light, and that feeble illumination gives a 
positive reaction and strong illumination a negative cne. 
Secondly, with the same intensity of illumination the reaction varies 
with the previous history and exposure to hght of the organism. 
Exposure to darkness or feeble illumination turns the organism so that it 
reacts positively, and previous bright illumination changes it so that it 
reacts negatively to a strength of stimulus to which it before acted 
positively. 
Thirdly, throughout these series of changes the original bias of the 
particular set of organisms persists, the other effects being superposed in 
a roughly algebraic summation. Thus the original trends towards positive - 
and negative in the two sets of organisms dawn out again at the end of - 
the experiment. 
Experiment III,—On velocity of movement in light of varying intensity | 
and colour. 
