STUDIES IN SPECIAL SENSE PHYSIOLOGY 401 



Summing up this rather difficult piece of work, I think the 

 reader will agree that : 



(1) The two commoner forms of partial colour-blindness are 

 distinguished one from another by a different responsiveness to 

 stimulation by long and medium wave-lengthened light. Protanopes 

 are relatively insensitive to long waves, deuteranopes to moderately 

 long waves. 



(2) Each is an example of dichromatic vision, using the term 

 in a purely experimental sense. 



(3) Each may be regarded as, to some extent, a reduction form 

 of normal vision, although, as we shall see later, this conclusion 

 cannot be pushed very far. 



The forms of partial colour-blindness just described are of 

 everyday occurrence, and their recognition of obvious practical 

 importance ; l another type less common, and therefore less com- 

 pletely studied, is that known as blue or blue-yellow blindness. 

 This condition, unlike the last two, is not as a rule congenital, 

 usually one-sided, and associated with definite pathological changes 

 in the retina ; it affects, generally, only a portion of the visual 

 field. Koenig's observations make it probable that this type also 

 is dichromatic ; 2 two suitably chosen lights will match the entire 



1 For the practical tests employed in the detection of colour-blindness, the 

 reader must consult the 8{>ecial treatises. It may he remarked that considerable 

 difference of opinion exists among ophthalmologists as to the reliability of the test 

 in common use. 



1 For the reader's convenience, I give a list of the chief papers dealing with 

 blue-yellow blindness. 



(1) J. Stilling, Beitrage z. Lehre v. den Farbeuemptinduugen Klinische 

 Monatsbl. f. Augenheilk. Jahrg. 13 (1875), 2nd Supp. p. 41, Jahrg. 14, 3rd Supp. 

 p. 1. Stuttgart, 1875-6. 



(2) Cohn, Studien Uber angeboreue Farbenblindheit, Breslau, 1879, pp. 139-148 

 (five cases with good bibliography). 



(3) Danders, Annales d'Oculistique, 12th series, vol. 4, 1880, p. 212. 



(4) Hohnyrtn, Centralbl. f. Augenheil., 5th Jahrgang, 1881, p. 476. 



(5) Hermann, Ein Beitrag z. Casuistik d. Farbenblindheit. Inaugural Disserta- 

 tion. Dorpat, 1882. (Not seen.) 



(6) V. Vintsciujau., Pttuger's Arch., vol. 48, p. 431. (A full account, without 

 theoretical bias, of a case in which no pathological changes were observed and a 

 precis of the observations contained in 1-5.) 



(7) V. yi>Utchyau, Pfl. Arch., vol. 57, p. 191. (Continuation of (6).) 



(8) Hering, Pfl. Arch., vol. 57, p. 308. (A study of v. Vintachgau's case, which 

 Hcring regards as yellow-blue blindness combined with a weak red-green sense.) 



(9) JYundt't Philosophische Studien, vol. 8, p. 173, 1892. (Not seen.) 



(10) Kotniij, Ueber Blaublindheit, Sit/ungsbericht d. Preuss. Akad. d. 

 Wissenschaft. in Berlin, 29th Juli, 1897, xxxiv. p. 718 (Pathological). 



2c 



