52 POPULAR SCIENCE MONTHLY. 



Another method of investigating the subject quantitatively which 

 I employed was to determine the distance at which small spots of dif- 

 ferent colors could be recognized. I found in Murray Island that 

 natives could see a red spot 2 mm. square at over 20 meters, while a 

 blue spot of the same size was confused with black at even 2 or 3 

 meters. Europeans, however, also recognized red at a much greater 

 distance than blue, and I have not at present sufficient comparative 

 data to enable me to say that there is any marked difference between 

 the Murray Islander and the European in this respect. 



These results do not show that these islanders are blue blind, but 

 they do show fairly conclusively that they have a certain degree of 

 insensitiveness to this color, as compared with a European. We have, 

 in fact, a case in which deficiency in color language is associated with 

 a corresponding defect in color sense. 



On the question of the cause of this insensitiveness there is room 

 for differences of opinion. It is, of course, possible that the insensi- 

 tiveness may be apparent only and may be merely due to lack of in- 

 terest, but there is, I think, little doubt that it depends on physiological 

 conditions of some kind. 



The Murray Islander differs from the Englishman in two important 

 respects; he is more primitive and he is more pigmented, and his insen- 

 sitiveness to blue may either be a function of his primitiveness or of 

 his pigmentation. In other words, it is possible that his insensitiveness 

 may depend on the lack of development of some physiological substance 

 or mechanism, which acts as the basis of the sensation blue in our- 

 selves, or it may only depend on the fact that the retina of the Papuan 

 is more strongly pigmented than that of the European. There is some 

 reason to think that this latter factor is the more important. We know 

 that the macula lutea in the retina, which contains the region of most 

 distinct vision, is pigmented, and that as a consequence of the reddish- 

 yellow color of its pigment, blue and green rays are more strongly ab- 

 sorbed than red and yellow; we have reason to believe further that the 

 macula of dark races is more pigmented than that of ourselves. 



The consequence would be that, in dark races, blue and green would 

 be more strongly absorbed, and consequently there would be a certain 

 degree of insensitiveness to these colors, as compared with red and 

 yellow. In the observations made with the tintometer, the patches of 

 color were so small that only the macula would have been stimulated. 

 The probability that the insensitiveness to blue depended, at any rate 

 partially, on the pigmentation of the macula lutea is increased by the 

 fact that the natives were able to recognize blue readily on the peri- 

 pheral retina. 



It would, of course, be wrong to make any wide generalization on 

 the basis of these observations. One would not be justified in directly 



