STUDIES ON SPECTRAL SENSITIVITY OF BIRDS. 



93 



Pfund has found two filters which work well in the determination of limits. 

 The filter for the red end consists of an aqueous solution of cyanin and potas- 

 sium bichloride placed in a convenient glass cell with plane parallel sides. 

 Such a cell was placed just behind the selecting unit, which was set at X = 7000. 

 This filter transmits 80 per cent of the light from X = 7000 up to 1^, but 

 excludes all light below X = 7000. When placed behind the slit, the retl surface 

 was clearly visible to me after 20 seconds of darkness adaptation.* The slit 

 in the collimater was set at 0.75 mm. and that in the objective at 0.52 mm. 

 The complete records of the chicks are shown in table 26. 



On the following day I set the slit at X = 7150 with other conditions exactly 

 as before. The light was quite faint to me. After 5 minutes' adaptation to 

 darkness the red surgerl in quite clearly. 



Table 26. 



X = 7000. 



Re.spoiis 



Remarks 



Left ] 

 Right 

 Right! 

 Right I 

 Left I 

 Right I 

 Right 

 Left J 



Right] 



Right! 



Left 



Left 



Right f 



Left 



Left 



Right] 



Right 



Right 



Left 



Left 



Right 



Right 



Left 



Lett 



fi2 per cent 



100 per e(>Mt 



|I waited before admitting animal until 

 1. light was visible to me. 



[I waited before admitting .auiii 

 1^ light was visible to me. 



I allowed this animal to make choice 10 

 seconds after turning out tantalum 

 light, regardless of whether I could see 

 it. It was below my thre.shold in 

 nearly all cases when he made his 

 choice. 



Chick D chose correctly 3 times, then made 3 consecutive errors, after which 

 he refused to respond even after long adaptation. I then turned the slit back 

 to X = 5480 (green of original training series) and gave him 5 trials; all were 

 correct and the average time of reaction was 2 seconds. 



Chick R chose twice correctly and then made three consecutive errors. 

 When tested on green of training series, 5 eoi'rect choices were made in an 

 average time of 2 seconds. 



Chick G would give only 8 responses; during these 8 trials two errors were 

 made. The animal chose with great difficulty. The average time of this chick 



*\Vhen it appeared it came in a burst of rerl light. There was no photochromatic interval 

 whatever. 



