TYPES OF ABNORMAL COLOR VISION. 



By Louis Bell. 

 Presented February, 11, 1914. Received, February 11, 1914. 



Despite the fact that so-called color blindness has been studied 

 for more than a century, little is yet known with respect to its real 

 nature or the various forms under which it appears. The present 

 investigation is a preliminary study of the latter made in the hope that 

 it may give at least some slight clues to the former. 



It is well known that about one man in 25 has a marked congenital 

 color defect. Without going into detailed statistics, the older data 

 show, from the work of Holmgren, B. Joy Jeffries, and the committee 

 of the London Ophthalmological Society, 3.82 per cent of color de- 

 ficient in 57398 males examined (Proc. Roy. Soc, LI, 319). This 

 figure is based chiefly on tests with Holmgren's wools, and is materi- 

 ally increased in many later investigations made with the color lan^ 

 tern and the spectroscope. Donders for example found 6.6 per cent 

 of color blind among 2300 railway employees in Holland, and even 

 this figure has been much exceeded. Bearing in mind that minor 

 color defects easily escape the wool test when applied in the ordinary 

 course of testing men for the red and green vision required for signal 

 lights, it is easy to realize that small variations from the normal, al- 

 though perhaps of much theoretical significance, readily escape notice. 

 These cases, too, have gone undetected on account of the frequent 

 acceptance of Hering's theory, which associates defects in red and in 

 green vision, a position now known in virtue of Burch's work on 

 temporary induced color blindness (Phil. Trans., B 191, 1) to be quite 

 untenable. This work and the earlier experiments of Rayleigh (Na- 

 ture, 25, 64) have opened up a wide field for the study of abnormalities 

 in color vision, which has of late years been somewhat explored. 

 That such are exceedingly common is in no wise better shown than 

 by a later paper of Burch (Phil. Trans., 199, B, 231) in which beside 

 giving various interesting cases of color defects, the author cites the 

 detailed examination of eleven cases of practically normal color vision. 



