66 WALTER S. HUNTER 



perimenter's breathing that the subjects might have utiHzed. 

 The dogs and raccoons did not rely upon the manner of being 

 released. This was proved by having different persons operate 

 the release. This control was not used with the rats. How- 

 ever, it is extremely improbable that these animals depended 

 upon cues from such a source. Moreover had they or any of 

 the reagents done so, their intervals of delay should have been 

 almost indefinitely great. It must be borne in mind that any 

 cues derived from the experimenter, in order to aft'ord extra 

 aid in the reactions, must be present at the moment of release. 

 This would make it possible for the animal to avail itself of 

 the cue after a delay of any length. If the cues were given by 

 the experimenter only at the beginning of the delay, the prob- 

 lem confronting the animal would not differ from that of delay- 

 ing with reference to the light. 



2. The reagents did not depend upon any after-glow of the 

 lights. When the lights were left on for one minute — a period 

 much greater than was ever used in the experiments proper — 

 and were then turned off, there was no appreciable after-glow 

 of the carbon filament that the experimenter could detect. 

 (In any event, such an afterglow would not persist long enough 

 to influence the longer delays of the reagents.) Hence any con- 

 tinued brightness of the boxes (considered from the reagent's 

 point of view) after the current was switched off must have 

 been due to the reagent's after-images. The possibiHty of 

 using these for cues will be considered below. 



3. The reagents did not depend upon variations in the tem- 

 perature of the boxes in making their reactions. After the 

 lights had been turned on for one minute in any box, the tem- 

 perature of that box was never raised more than a degree centi- 

 grade. Indeed only occasionally could any change of tempera- 

 ture be detected. The "headlong" manner in which the ani- 

 mals reacted to the boxes, together with the fact that they 

 oriented toward the light immediately upon its appearance 

 indicate that they were not governed in their reactions by the 

 slight variations in temperature. Yoakum'' found that rats 

 could discriminate differences of 16° C, but even then their 

 behavior was the result of long special training. His squirrels 



■" Yoakum, C. S. Some Experiments Upon the Behavior of Squirrels. Jour. 

 Comp. Neur. and Psych., 1909, vol. 19, p. 565. 



