176 COLOR-BLINDNESS IN ITS RELATION TO 



to the person examined, he being required to name the colors or their 

 value as signals, his chromatic sense could not be judged by his answer. 

 For we have seen, on one side, that the color-bliud can guess correctly 

 in such cases, and, on the other hand, it is scarcely necessary to sny that 

 the normal observer might make a mistake in the name, either from negli- 

 gence, through inattention, or simply by a lapsus livguce. How many 

 times, then, must the trial be repeated to secure positive results ? How 

 often must the individual make mistakes to be considered color-blind? 

 How many times may he make them without being considered color- 

 blind? Evidently there is no categorical answer to these questions. We 

 are therefore authorized to conclude that the examination by means of 

 railway-lanterns, for discovering color-blindness, must be considered for 

 several essential reasons as an impracticable method, and consequently 

 to be rejected. The use of flags, for the same purpose, is still worse. 

 A general principle, applying to every examination of the chromatic 

 sense, is that such examination should not at first endeavor to trace the 

 connection of the chromatic sense with signals of any kind whatsoever, 

 but have in view only the discovery as to whether the subject is or is 

 not color-hlind, or whether the chromatic sense is defective or normal. 

 While none of the various methods proposed can be condemned as ab- 

 solutely barren, there are several which, used alone, never give positive 

 results, or give them only in a limited number of cases, or else cause 

 so great a loss of time, and are so inconvenient, that they ought to be 

 rejected from this consideration alone. We class amongst tbese methods 

 all those which, as in the examination by means of the lantern, have a 

 tendency, in principle, to place before the one to be examined different 

 colors or colored objects to be named by him. The real question is not 

 to discover the degree of skill comparatively attained by each one in 

 correctly naming the colors, but the manner in which he sees them, or, 

 in other words, the nature of his chromatic sense. Any method fultill- 

 iug this requirement must, in principle, be based upon the comparison 

 between difl'erent colors, and an investigation into the causes of the con- 

 fusion of the color-blind about several of them. 



An example will more clearly illustrate our idea and show its impor- 

 tance. Let us take a green-blind individual j we know by experience 

 that he confuses or finds a perfect resemblance between tbe shades of 

 three colors very different to the normal eye. I allude to purple, green, 

 and gray. The reason of this is very simple according to the theory; 

 the green-blind is void of the organ for perceiving green. Purple, green, 

 and gray are, in reality, the same color to the eye of the green-blind, 

 but he has heard three names given to these colors under difl'erent cir- 

 cumstances. The result of this will be that he will in his turn designate 

 this color sometimes by one and sometimes by another of these names, 

 or else he will only use one, especially the one he first remarked or heard 

 most frequently applied to this color. If the subject use all three names, 

 he will apply them correctly in some instances and incorrectly in others. 



