382 Report of the Committee on Colour- Vision. 



rules arises from misunderstanding, or lack of practice with 

 coloms, or, finally, from a true chromatic defect. To in- 

 clude all that is green would render the test tedious and 

 unpractical. In fact, no little judgment has been exercised in 

 the selection of the very lightest shade of the green proposed as 

 a test-colour; for it is exactly what the colour-blind most 

 readily confounds with the colours (1-5) of the plate. If the ex- 

 aminee were allowed to depart from the narrow limits established 

 by the trial, it would include every shade of green ; the result 

 of which would be that he would prefer to select all the vivid 

 shades, and thus avoid the dangerous ground where his defect 

 would certainly be discovered. This is why it is necessary to 

 oblige him to keep within certain limits, confining him to pure 

 green specimens, and, for greater security, to recommend him 

 uo select especially the lightest shades ; for, if he keeps to the 

 darker shades, as many try to do, he readily passes to other tones, 

 and loses himself on foreign ground, to the great loss of time 

 and of certainty of the test. What we have just said of green 

 applies also, of course, to purple. 



" The principle of our method is to force the examinee to 

 reveal, by an act of his own, the nature of his chromatic sense. 

 Now, as this act must be kept within certain limits, it is evident 

 that the examiner must direct him to some extent. This may 

 present, in certain cases, some difficulty, as he will not always be 

 guided, and does either too much or too little. In both cases the 

 examiner should use his influence, in order to save time and gain 

 certainty ; and this is usually very easily done. This intervention 

 is of course intended to put the examinee in the true path, and is 

 accomplished in many ways, according to the case in point. 



" We will here mention some of the expedients we have found 

 useful : — 



" (A) Interfering when the Examined select too many Colours. 



" It is not always easy to confine the one examined within the 

 limits of the method. He easily slips amongst the sorted colours 

 for the first test, for example, a yellow-green or blue-green skein 

 among the others, and, as soon as there is one, others follow 

 usually; and it thus happens that in a few moments he has a 

 whole handful of yellow -green, a second of blue-green, a third of 

 both these shades at the same time. Our procedure has assisted 

 us in more than one case of this kind. 



" (a) When the person examined has begun to select shades of 

 one or several other colours than those of the sample, his ardour 

 is arrested by taking from him the handful of skeins he has 

 collected, and asking him whether his eye does not tell him 

 there are one or several which do not match the others, in 

 which case he is solicited to restore them to the pile. He then 

 generally remarks that there is some obscuration, and proceeds 

 in one of the following manners : — 



" 1. He rejects, one after the other, the foreign shades, so 



