234 SECTIONAL ADDRESSES 



Table V. 



Schaaff's Mosaic Plates. 



Frequency in percentages of normal and colour-blind responses for N, 



N — and colour-blind groups. 



N = 271 males. N — =46 males. C. B. = 40 males. 

 C = correct both circles : |C = one circle correct, one wrong : 



W = wrong, both circles. 



per cent, of the colour-blind group. These two plates alone, number 1 1 

 and number VI, are severe tests of colour perception. 



Of the test as a whole, 43 per cent, of the N group made a perfect score, 

 that is, pointed out the gap in each circle correctly. In the N — group, 

 only 24 per cent, passed, and in the colour-blind group no individual 

 made a perfect score. Sometimes, in all groups, the shape of the circles 

 could be recognised but the gaps could not be located. When the rings 

 are recognised, but not the gaps in certain tables, only slight weakening 

 of the colour sense is indicated, but when the rings are not recognised, the 

 defect is of a more serious nature. In the instructions accompanying the 

 mosaics, the following words appear : ' Quiconque ne discerne pas les 

 anneaux et les brisures dans les dix tableaux, n'a pas le sens chromatique 

 normal.' 



The final estimate of this test is that it can be recommended as a fairly 

 satisfactory test of colour blindness. 



A supplementary test, devised by Schaaff and Blum, consists of 30 cards 

 on which are diamond-shaped spots. Some of the cards contain one 

 colour only, but in varying shades, green of more than one shade, or red, 

 or grey. Some of the cards have more than one colour on them. The 

 subject is asked to sort the 30 cards into piles — a pile of cards in which 

 all the spots are red, a second pile in which all the spots are green, and 



