2 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
CONCLUSIONS 
1. The characters of the response of an organism by movement to 
light are not constant for a given organism, but vary for the same 
organism at the same time according to the intensity of the hght and the 
previous history of the organism in regard to light. As a general rule, 
the organism is positive to feeble light and negative to stronger light, and — 
for a constant intensity of light at a given moment previous darkness or 
weak stimulation tends to turn organisms positive, and previous exposure 
to bright hght turns them negative. 
2. Both the positive and negative behaviour to light may be 
explained on the basis of one chemical action of light upon the cell 
(a katabolic one). The positive state indicates that the speed of reactions 
in the cell hes below a certain value, which may be called the optimal 
value, and the negative state corresponds to a speed of reactions in the 
cell above the optimal value. In the former case the sentient surfaces 
are turned into the lhght to increase velocity of reaction up towards the 
optimal value; in the latter case the sentient surfaces are turned away 
from the light so as to decrease the velocity of the reactions down towards 
the optimal value. 
3. Asa result of the orientation so caused, there arises movement of 
the organism towards or away from the source of light, but such 
orientation is not a fixed orientation, but rather a steering action; the 
animals as a result do not remain in one fixed plane or direction of 
movement, but the net result of the movement is that the organisms move 
to or from the light. When the movement is finished the organisms 
(plaice) may lie im all possible planes of orientation to the light. 
4. Movement towards or away from the light has in some organisms 
(Nauplii of Balanus) an associated movement upwards or downwards. 
‘These two movements would coincide together in natural movements of 
the organisms under the influence of ight alone in the sea. 
5. In the case of Naupli of Balanus, addition of small amounts of ~ 
acid or alkali was not found to alter the reactions to light. 
6. The rate of movement of the organism (Nauplii) is almost the 
