Mast, Light Reactions in Lower Organisms. l6i 



ical reactions, based upon possible chemical changes in the organ- 

 ism. But since the chemical changes are purely hypothetical, 

 this explanation must be, of course, considered merely as a sug- 

 gestion. 



If our explanation proves to be correct, the process of acclima- 

 tization must be the process of such changes in the organism that 

 the neutral condition will be produced when the relative amount 

 of the substances represented by X and T is changed. 



Temperature changes, mechanical agitation, or any other agent 

 which would in any way affect the chemical reaction between X 

 and T would, of course, influence the change in the sense of reac- 

 tion, and thus we should have a possible explanation of the effect 

 of such agents on the change from positive to negative reaction 

 and vice versa, recorded in the literature on the subject. 



13. EFFECT OF TEMPERATURE ON CHANGES IN SENSE OF 



REACTION. 



On August 17, 1904, Volvox colonies which were strongly posi- 

 tive were put into a small aquarium containing water about 5 mm. 

 deep and exposed to light from a group of three 222 volt glowers, 

 15 cm. from the aquarium. The light intensity in the aquarium 

 was approximately 4000 candle meters. The colonies were there- 

 fore in an intensity which was nearly optimum. The water in the 

 aquarium was then slowly heated to 45° C. As the temperature 

 increased the organisms became slightly more active but showed 

 no indication of becoming negative. When the temperature 

 reached 45° nearly all were dead. This experiment was repeated 

 and the temperature raised to 51°, a temperature which p:oved 

 fatal to all the colonies. The results in the second experiment 

 were similar to those in the first. It therefore seems evident 

 that change in temperature does not induce reversal in the sense 

 of reaction in Volvox. This, however, does not mean that change 

 in temperature may not affect reaction to light; indeed, it is more 

 than probable that it does, for at low temperature all light reac- 

 tions cease. 



These results agree with those obtained by Parker on Copepods 

 ('02, p. 117) and by Yerkes ('03, p. 375) on Daphnia pulex, but 

 they do not agree with those obtained by Loeb ('93, p. 91), who 

 found that the sense of reaction in Polygordius larvae was changed 

 from positive to negative by a change in temperature from 24° C. 



