RESEARCHES BASED UPON THE THEORY 267 



relatively yellow-sighted saw farther to the red end of the spectrum than 

 the blue-sighted, and the violet end was less saturated to them. The 

 yellow-sighted appeared to have more sensitive chromatic substances 

 than the blue-sighted. 



Hering compared the sensations of the two types of " red-green ' 

 blindness, i.e., protanopes and deuteranopes, with those of the anomalous 

 cases. He showed that the red-green blind with unshortened spectrum 

 (deuteranopes) were analogous to the yellow-sighted in their grey matches. 

 Similarly the red-green blind with shortened spectrum (protanopes) 

 were analogous to the blue-sighted 1 . The colourless green of the 

 neutral point, matched with a red-violet mixture, required a greater 

 intensity of the green in the so-called green-blind than in the so-called 

 red-blind. Hering specially recommends this match for statistical 

 purposes, but unfortunately it is much vitiated by pigmentary absorp- 

 tion. Another typical difference was the greater luminosity of the red 

 end of the spectrum for the so-called green-blind, the red-blind requiring 

 a much darker grey luminosity-match. These and other effects were 

 attributed to a weaker blue sensation in comparison with the white 

 sensation in the red-blind as compared with the green-blind. Similar 

 differences were found in peripheral vision. It will be noticed that 

 Hering's researches confirmed those of Konig and other observers, but 

 his interpretations are different. 



Hering's researches on the totally colour-blind 2 first proved the 

 identity of their luminosity curve with that of the normal dark-adapted 

 eye for low intensities. He regarded this fact as strong confirmation 

 of his estimates of the white valencies of lights for the dark-adapted 

 eye. He also found that the sensitiveness of the totally colour-blind 

 eye for slight differences of luminosity was the same as that of the normal 

 achromatic scotopic eye. Hess and Hering 3 and their followers have 

 strenuously opposed the view that the totally colour-blind have a central 

 scotoma, but as we have seen, too much stress has been laid upon the 

 negative evidence. 



We have seen (v. p. 256) that Hering has attempted to explain the 

 differences of the photopic and achromatic scotopic luminosity curves 

 by the theory of the specific brightness of colours. Tschermak 4 does 



1 Cf. Rose, Arch f. Ophth. vn. 2, 72. 1861. 



2 Hering and Hillebrand, Sitz. d. Wiener Akad. xcvm. 70, 1889 ; Hering, Arch. f. d. 

 ges. Phijsiol. XLTX. 563, 1891. 



3 Arch.f. d. ges. Physiol. LXXI. 105, 1898. 



4 Ibid. LXX. 297, 1898 ; LXXXII. 559, 1900. 



