106 FLETCHER, COWAN AND ARLITT 



light from the stimulus was reflected on the walls of the room. 

 The following apparatus was found eminently satisfactory and 

 was used throughout the rest of the series of experiments with 

 light. It consisted of a one-candle power incandescent light 

 connected in series with a rheostat and so arranged that by 

 varying the resistance of the circuit the light could be adjusted 

 from zero to full intensity. The stimulus was found to give 

 best results when adjusted to about one-half full intensity. The 

 apparatus was on a table covered by a cloth of dull black ma- 

 terial having a minimum refractive power. The experiments 

 were conducted at night. 



At the time of the second hatch all light was excluded from 

 the incubator from the nineteenth to the twenty-fourth day. 

 On the evening of the twenty-fourth day ten chicks, five normal 

 and five alcohol, were removed from the incubator one at a 

 time, numbered and marked with aluminum pigeon markers 

 and placed on the table, eighteen inches from the stimulus. 

 They were so placed that their heads were turned slightly away 

 from the light. Three alcohol and two normal chicks reacted 

 positively. Turning and facing the stimulus, they walked toward 

 it. The other chicks walked diagonally or directly away from 

 the light. Two normal and one alcohol chick walked off the table. 



On the following night the same procedure was repeated 

 with the ten chicks previously tested and eleven others, four 

 normal and seven alcohol, which had been too weak to be 

 handled on the first night. Of the ten previously tested, eight 

 reacted positively. No. 36, which had reacted slowly and Nos. 

 4, 6 and 35, which had not reacted at all, walked directly to 

 the light as soon as placed on the table. Of the four normal 

 chicks not tested before one reacted positively to the stimulus, 

 walking directly to the light and placing its bill against it; the 

 other three walked away from the light. Of the alcohol chicks 

 not tested before three immediately moved toward the light, 

 one after an interval of three minutes, and the other three walked 

 around the table, going sometimes towards, sometimes away 

 from the light. 



The twenty-one chicks were tested again on the third day. 

 Normal chick No. 3 and alcohol No. 34, which had reacted 

 positively on the first and second days, did not react on the 

 third; normal No. 4 reacted on the second, but not the first 

 and third days; alcohols No. 21 and No. 33 reacted on the 



