120 J. C. DeVOSS and rose ganson 



at all. During hundreds of our first trials no confusions did 

 occur, for we used Hering grays paired with Bradley colors. 

 Discrimination was prompt and apparently this was due to the 

 difference in texture between the two types of paper, for we 

 later found numerous confusions. As shown by the cats' re- 

 sponses, pieces of ordinary cambric may be found which are so 

 near the texture of the Bradley papers (when both are placed 

 behind clear glass) that they are not discriminable by the animals. 

 This is not true of Hering grays with Bradley papers. In such 

 pairs we think that the Hering papers are not suitable for the 

 study of any but the most defective eyes, because of their granular 

 texture. This opinion is based on tests of the whole series of 

 Hering grays with three cats. Miss Washburn 6 obtained admir- 

 able results with Hering grays and Bradley colors in investigating 

 the vision of the rabbit. But as the rabbit has medullated 

 nerve fibres passing in front of the retina 7 we should imagine 

 that that defect would make the rabbit's eye very poor for the 

 discrimination of textures. 



In order to avoid awkward circumlocutions we have used 

 such subjective terms as "confusion," "discrimination" (both 

 "easy" and "difficult") etc. The reader will observe, however, 

 that in every case these terms signify a definite objective con- 

 dition, measured by the responses of the animals. 



APPARATUS AND METHOD 

 The apparatus was that used by Cole and Long (p. 667). It 

 was painted dead black and had black partitions between the 

 glass holders. These partitions were necessary because in our 

 experiments the colored papers were placed within the glasses. 

 This permitted the possibility of a certain amount of reflection 

 from a glass to the one beside it in case no black partitions were 

 interposed. Since one cat seemed to make the choice of a glass 

 by the position of the thumb-buttons, which fasten the levers, 

 the buttons were concealed by shields of black cardboard cut 

 for the purpose. The glasses mentioned were the feeding vessels 

 and were ordinary jelly glasses, selected from a large assortment 

 for clearness, freedom from flaws, and uniformity of size and 

 shape. By means of the levers these glasses were clamped with 



6 Washburn, M. F. and Abbot, Edwina. Experiments on the brightness value of 

 the red for the light-adapted eye of the rabbit. Jour. Animal Behavior, vol. 2, 1912. 



7 Howell, W. H. Physiology, 1908, p. 319. 



