498 ADAPTATIONS TO PHOTIC QUALITY 



Along with this blue-blindness, a sensitivity to red greater than that of 

 man seemed also to be demonstrated by this early work. 



Between 1916 and 1926, the experiments of Hahn, Honigmann, and 

 Blasser painted a different picture. By staining rice grains with different 

 dyes or by illuminating them with colored lights, gluing down the grains 

 to which it was desired to train the birds negative, they showed that the 

 domestic hen does see blue and violet, though weakly. She does have a 

 partial, relative blue-blindness, which increases during growth, presum- 

 ably because of deepening oil-droplet pigmentations. More important 

 however is her 'blue-shyness', which must be overcome by patient training 

 before she is convinced that blue objects can be good to eat — the best 

 explanation of Hess's results is simply that for a hen, there are no blue 

 foods in nature! 



In the meantime, some very careful work had been done in this coun- 

 try by Watson and Lashley in 1915 and 1916, but because of the war it 

 went unnoticed abroad for years. They used superlative apparatus afford- 

 ing brilliant beams of pure spectral lights. With a training technique, 

 Watson was able to fix the chick's spectral limits as lying between 

 A,700m^ and A,715m[i at one end and between A,395m|i, and A,405m[X at 

 the other. His preliminary experiments upon thresholds for colors indi- 

 cated that these were about the same as in man, except for the far red to 

 which the chick was somewhat more sensitive. Similar work with the hom- 

 ing pigeon revealed spectral limits of A,420m|l and A,712m[i, indicating 

 that Hess had also been in error in claiming the pigeon to be blind to 

 blue and violet. 



Lashley carried on from here, using essentially the same apparatus and 

 procedure. He was able to train his game bantam cocks positive to red 

 (7.650m[x), yellow (X588mp, and A,565mp,), green (A,520m|i) and blue- 

 green (A,500m^), and to discriminate each of these from other colored 

 and white lights of any brightness. By changing the wavelength of the 

 negative stimulus, making it closer and closer to that of the positive one 

 until discrimination failed, and repeating this procedure in various parts 

 of the spectrum, he was able to plot a curve of hue-discrimination which 

 proved to have the same number of maxima, in about the same locations, 

 as the corresponding graph for man. The hen's color-vision system is cer- 

 tainly trichromatic, probably essentially identical with our own — though 

 it was independently evolved (consult Fig. 156, p. 519) ; and the filtering 

 action of the oil-droplets is of course a modifying factor. 



Simultaneous color-contrast has been shown to exist for the hen, just 



