STUDIES ON SPECTRAL SENSITIVITY OF BIRDS. 



95 



Both D and R broke clown completely and took up right-hand position 

 habits. I then immediately gave them X = 4050, with conditions as in previous 

 tests, with the results shown in table 30. 



Evidently under conditions such as I have been describing the violet limit 

 lies between X = 4050 and X = 3950 for these two animals. The stimulation 

 was in every case over my threshold. Furthermore, the animals were ad- 

 mitted 10 seconds instead of 5 after turning out the light. 



Much to my surprise chick G gave different re- 

 sults. He was tested under the same conditions as 

 D and R with X = 3950. The light to which he re- 

 sponded was never above my threshold. I give his 

 record in full in table 31. In every trial in which 

 10 seconds were given, the animal responded cor- 

 rectly. It is evident that the threshold is a flexible 

 kind of thing and dependent naturally upon adapta- 

 tion. The limit for G for long adaptation is certainly lower than X = 3950, 

 but for 5 seconds' adaptation at the present intensity X = 3950 is about 

 the limit. 



On the whole, I think it perfectly safe to conclude that chicks do not have a 

 spectrum shortened at the violet end, nor yet do they show any special sensi- 

 tivity in the violet. The experiments of Hess* and of Katz and R^vfezf 

 lead them to believe that the chick is practically blind to blue and violet rays. 



Table 31. 



As will be seen by the later exijeriments reported in this paper, the chicks are 

 probably as much stimulated by these rays as the human being. It is barely 

 possible that the difference in the strain of chick used is responsible for the 

 differences in our results. I think, however, that their method of allowing 

 the chick to pick up grains of food illuminated by the different rays is a faulty 



*Hess, C. Untersuchuugen Uber Lichtsinn und Farbensinn der Tagvogel. Archiv f. Augen- 

 keilkunder, Bd. 57, S. 317. 



tKatz und Rfvesz. Experimentell-Psyehologische Untersuchuugen mit Huhner. Zeit. !. 

 Psy., 1909, S. 93. 



