2o8 SECTIONAL ADDRESSES 



2,000 boys, a frequency of 7-95 per cent. Kilborn and Beh,^ testing 

 Chinese male students, found 6-3 per cent, of them to be red-green 

 bHnd, and Hsiao,* examining Chinese children, gives his figure as 

 5 • 57 per cent, among the boys. Lorenzo and McClure ^ found, of a 

 group of men tested at the University of Toledo, that 9 per cent, were 

 colour blind, and Garth,® testing children and students in Turkey, a 

 percentage of 5-3. Among groups of medical students, Macklin' found 

 about II -o per cent., and Tocantin and Jones ^ found 12-8 per cent, 

 who were red-green colour blind. Miles ^ testing university men, 

 gives 8-4 per cent, as colour blind, and among a group of dry goods 

 salesmen he found a percentage of 7-2. Out of 360 candidates applying 

 for acceptance as apprentice printers, examined by the present writer, 

 the percentage of red-green colour blinds was 7-5, this figure being 

 exclusive of the colour weak and the anomalous. 



At the present day, there are said to exist three varieties of colour 

 blindness. And while we are primarily concerned with the red-green 

 variety only, it seems desirable for completeness to indicate briefly the 

 nature of the other two types. They are not of equal importance either 

 from a theoretical or from a practical point of view. 



Total colour blindness or Achromatopsia (sometimes called Achroma- 

 topia) is not of frequent occurrence, only about eighty cases having been 

 described up to date.^" To the totally colour blind the spectrum is a 

 colourless band, differing only in luminosity. Red may appear black, 

 orange dark grey, yellow light grey and so on. To such a monochromat ^^ 

 bright light is extremely dazzling, in fact, ordinary illumination is some- 

 times unbearable, but in dim illumination he can see fairly accurately. 

 Achromatopsia is often accompanied by nystagmus and by poor central 

 vision. In many cases an absolute central scotoma exists which means 

 absolute blindness to light at the fovea as well as to colour. Parsons 

 states that ' whether all cases have an absolute centrol scotoma or not, 

 it is certain that foveal vision is very defective, even as compared with 

 parafoveal, as is admitted by Hess.' ^^ 



To the totally colour blind the region of maximal brightness lies in 

 the green, a condition similar to that found in the dark-adapted or 

 scotopic eye. The luminosity curve of the monochromat agrees very 

 closely with the normal achromatic scotopic luminosity curve. There 



* Science, 1934, 79, 34. * /. Applied Psychology, 1935, 19, 641-646. 

 8 Ibid., 320-330. 8 Science, 1936, 84, 85. 



' Canad. Med. Assoc. J ., 1933, 29, 302-303. 



* Amer. J. Med. Sci., 1933, 185, 243-249. 

 ® The Personnel J., 1931, 9, 437-449. 



1" For a description of a case of total colour blindness, see Snyder, Amer. J. 

 Psy., 1929, 41, 398-411. 



^1 This term is objected to by E. Murray, who writes : ' Monochromatic is merely 

 a physicist's tag signifying that in this type of deficiency any wave-length of light 

 can be matched against any other. Actually the vision of the subject is achro- 

 matic, without any colour quality whatsoever. No genuine monochromasy in 

 the descriptive sense is, for theoretical reasons the compounding of white from 

 chromas, admissible.' Quoted from article in Amer. J. Psy., 1930, 42, 117-127. 

 Color Problems : the Divergent Outlook of Physicist and Psychologist. 



^2 ' An Introduction to the Study of Colour Vision,' 2nd Ed., p. 199. 



