146 LESLIE B. AREY 



All the (Xperinieiits of i)revious workers on the effect of tem- 

 perature have been performed in the dark and I, therefore, set 

 about to discover what results would be obtained in the light. 

 The only change in the apparatus from that previously described 

 was that a 20 litre jar replaced the metal tank; this, when filled 

 with water at the desired temperature, performed the necessary 

 heating function while its transparency did not interfere with 

 the entrance of light into the inner chamber. Experiments 

 were made at the same temperatures as in the dark — 3° to 5°C., 

 16°C. and 33°C., but the results were, for the most part, condi- 

 tions of uniform expansion independent of temperature. 



It was observed that when frogs were subjected to a low 

 temperature they became quiescent and tended to keep their 

 eyehds closed. Although the lower lid (the only one which 

 is movable to any extent) is more or less transparent, the possi- 

 bility of its influencing the results led to its removal in a number 

 of instances; no difference, however, was obtained by the ob- 

 servance of this precaution. From these results, therefore, 

 we conclude that in darkness, temperature is the controUing 

 factor, while in the light temperature is subordinate to the 

 stronger stimulus, light. 



At this juncture a doubt arose as to the exact temperature 

 the frog's retina was experiencing while in the apparatus. It 

 is well known that at the surface of the frog's body rapid evapora- 

 tion can take place; hence it is perfectly conceivable that the 

 rate of evaporation in the temperature chamber might be such 

 as to keep the body temperature for some time considerably 

 below that of the surrounding air. This possibility was first 

 checked by taking the oesophageal and rectal temperatures of 

 animals that had been subjected to various temperatures in the 

 apparatus for several hours. The recorded temperature, how- 

 ever, was nevei found to vary more than a fraction of a degree 

 from that of the air in the containing chamber. 



To be absolutely certain on this point, a prolonged set of ex- 

 periments was made in which the frogs were immersed in water 

 media of appropriate temperatures. It is certain that after a 

 short time the animal, as a whole, must assume the temperature 



