268 J. S. NICHOLAS 



S. The reactions of normal animals in the dark room. {In 



aquarium) 



The animals were dark adapted for two days before the experi- 

 ments were undertaken and were given no food for three days. 

 After dark adaptation, the animals are noticeably more sensitive 

 to handling and the time required to come to rest is lengthened 

 appreciably. A dim red hght of minimum intensity, just suffi- 

 cient for the observer, after a dark adaptation of forty minutes, 

 to see the animal in profile, Avas used for the observations. The 

 intensity was so weak that the figures upon a watch dial could 

 be read with difficulty just in front of the screened light source. 

 This degree of light is probably below the visual threshold of 

 Amblystoma (Arey, '19), as evidenced in the reactions of the 

 animals during the period of observation preceding the actual 

 experiments. Ordinarily, with one side of the aquarium more 

 brightly illuminated than the other, the animal, particularly if 

 hungry, will tend to move about th*e sides of the aquarium with 

 a preference for the brighter side, being often attracted to its 

 own reflection in the glass wall, as well as by shght visible move- 

 ments at the side of the aquarium. Under the dark condition, 

 the animal moves slowly up and down until it is stopped by the 

 aquarium wall, then turning, it may proceed down the center 

 of the aquarium, showing no particular preference for the wall. 



Reactions to motionless objects. The test bags were used as in 

 the preceding section and the description of one individual case 

 will show the procedure with the unvarying positive result 

 (table 1, 3 a). 



Trial 1. Animal B. Tested by the offering of the two test 

 sacks. The earth worm bag and the sand bag were placed at 

 opposite ends of the aquarium. The animal shows the character- 

 istic motor reaction soon after the introduction of the material, 

 but seems unable to locate it. Finally locates the object. Posi- 

 tions of bags reversed and operation repeated. Animal swims 

 restlessly about for some time before approaching object, noses it, 

 and seizes it. As an additional test, a glass vial containing freshly 

 cut earthworms was placed in the aquarium. The animal 

 immediately becomes restless and, after swimming about for 



