SENSE ORGANS. j 4 j 



III. 



See incorrectly. 



a. Scarlet = red and yellow — i. c, gray and yellow = dark 

 brown. 



b. Orange = red and yellow — i. e., gray and yellow = lighter 

 brown. 



6. Bluish green =r blue and green — i. e., blue and gray = slate- 

 blue. 



d. Yellowish green = yellow and green — i. e., yellow and gray 



= brown. 

 j. Purple = red and blue — i. e., gray and blue = slate-blue. 



Tests. — It might seem that so striking a phenome- 

 non needs no test. Every one must know it. But this 

 is far from the fact. On the contrary, a man may be 

 color-blind unknown to himself and to his friends. He 

 may have observed some instances of curious confusion 

 of colors, but these are attributed to imperfect knowledge 

 of color names. In the case of persons in responsible 

 positions, such as locomotive-engine drivers, ship steers- 

 men, etc., where color signals are used, it is very impor- 

 tant that ability to see colors correctly should be tested. 

 The simplest test and one of the best is a box full of 

 skeins of yarn of all colors and shades, and several of 

 each. Such a box is placed before the person to be 

 tested, and he is directed to sort them and match the 

 colors. All normal-sighted people would match them 

 alike and correctly, but the color-blind make the most 

 extraordinary mistakes. Certain shades of red and green 

 and gray are put together as the same ; similarly certain 

 shades of scarlet and brown or purple and slate-blue. 



By these tests the remarkable fact is brought out 

 that this defect is much more common in men than in 

 women. About one in every twenty-five men are more 

 or less color-blind, while among women hardly one in a 

 thousand is thus affected. 



