106 Kansas academy of science. 



well established, even without great accuracy of data, that among civilized nations 

 color-blindness is at present almost equally common. 



Second, among uncivilized people, Dr. Favre's results from Algiers, already al- 

 luded to, show 414 examined, and only 2.6 per cent, color-blind. 



Dr. Fox reports 161 young Indians tested, and only 1.81 per cent, color-blind. 



These percentages, so low compared with those for civilized people, suggested to 

 us that color-blindness may be a product of civilization, and have led to our tests 

 here reported. 



At the Haskell Institute, at Lawrence, Kansas, are several hundred Indians, rep- 

 resenting many tribes. These we have recently examined by Holmgren's method 

 with Berlin worsteds. Out of 418 tested — 285 males and 133 females — only three 

 cases of color-blindness exist, or only .7 of one per cent. These three are full-blooded 

 Indians of the Pottawatomie, Pawnee and Crow tribes. Of these, two have defective 

 color-sense for red and one for green. 



The Indians of the School are about equally divided as full-bloods and half-breeds. 

 It seemed to us that the half-breeds showed more instances of blunted color-sense 

 than the full-bloods. This was evidenced in more frequent and prolonged hesita- 

 tion among them in comparing the colors than among the full-bloods. 



If this be confirmed by more extended examinations, it would, in conjunction 

 with the low percentages obtained as above, be an argument on the theory proposed 

 by us, that defective color-vision is in some way the product of civilization. 



The use of tobacco suggests itself as a possible cause. This would explain also 

 the low percentage among females. It leads also to the thought of increase of color- 

 blindness in males in future generations. But the data are at present too meager 

 to more than suggest this explanation. 



It is certainly not accidental that nearly every case of color-blindness is for red, 

 few for green, and seldom one for violet. Why are the defects thus limited, at pres- 

 ent at least, to the longer wave-lengths of light? 



The Young-Helmholtz theory of color-perception will locate the affection in that 

 layer of the retina corresponding to the first of the three primary sensations of color. 

 But why this special layer, with few exceptions, is the only one affected, has at pres- 

 ent no explanation. 



The law of heredity indicates increasing sensitiveness in those nerves which are 

 subjected to special use through many generations. It seems reasonable that this 

 must lead to a more perfect color- sense in females; but among males there will 

 probably be an increase, in future generations, of the number of cases of defective 

 color-sense. 



Physical Labobatoky, November 1, 1888. 



STATISTICS ON COLOR-BLINDNESS AMONG THE STUDENTS AT THE 

 STATE AGRICULTURAL COLLEGE. 



BY C. M. BREESE, 

 Kansas State Agricultural College, Manhattan. 

 The test used in conducting this experiment was that known as the Holmgren 

 method. The operator had tumbled a great number of small pieces of yarn of all 

 the various colors and shades obtainable, in one pile. These we will term the yarns 

 of confusion. A yarn of a j)ure, light-green color was given the person to be exam- 

 ined, and he was asked to select from the colors of confusion several pieces of yarn 



