REYIEWS — RESEARCHES ON COLOUR-BLINDNESS. 155 



to the former, who live in regions bereft of vegetation during the greater portion 

 of the year, and presenting to the eye little but the dazzling monotony of ice and 

 snow. The sense of colour must, to a g'-eat extent, lie dormant in those so cir- 

 cumstanced, and become dulled through want of exercise. The tribes in question 

 and others in similar latitudes seem very indifferent to colour, as an addition to 

 their dress or ornaments. 



What are the physical causes •which give rise to this strange pecu- 

 liarity ? Some philosophers have sought to ascribe it to a malforma- 

 tion of the eye, or to some coloration of one or more of the mem- 

 branes, the choroid or the retina. Dalton attributed his own colour- 

 blindness to a blue tint in the vitreous humour, on which supposition 

 he successfully explained most of the facts in his own case ; an ex- 

 amination however after death shewed that this humour was not blue. 

 Other theories of this kind may be set aside simply by the fact that 

 Albinoes are normal as regards colour. Nevertheless it can hardly 

 be doubted that variations in the prevailing tinges of the humours 

 and membranes of the eye must produce chromatic peculiarities of 

 vision ; which would fall, however, under a different class than those 

 now considered. Dr. "Wilson discusses these points in detail with 

 much acuteness and ingenuity, and closes his review with the fol- 

 lowing remarks : — 



" I am not disposed to assert that colour-blindness, of the kind Dalton and his 

 fellows exhibited, can be occasioned by such modifications in the colour of the 

 membranes of the eye as I have drawn attention to. But an extreme chromatic- 

 equation, not always distinguishable in its practical manifestation from veritable 

 colour-blindness, may certainly be occasioned by the varying condition of the mem- 

 branes referred to, and on this account I have, in the introduction to this discus- 

 sion, spoken of such manifestations as deserving to be ranked under a special 

 chromatic theory of colour-blindness. 



" I close this section with the expression of the hope, that the colour of the 

 membranes within the eye-ball will now be an object of more frequent and minute 

 examination by physiologists, than it has hitherto been. My friend, Dr. Beddoe, 

 has indirectly supplied much interesting information on this subjeet, in his little 

 work recently published,* containing the results of an examination during life, of 

 the colour of the eyes and hair of some 5000 of the Scottish people, representing 

 nearly all the districts of their country. According to the observations of John 

 Hunter, already quoted, in which physiologists generally concur, a dark choroid 

 and dark hair go together, aud vice versa. In the future enumeration, accordingly, 

 of cases of colour-blindness, it is desirable that the colour of the hair should be 

 recorded, as it cannot be expected or desired that the majority of the colour blind 

 should speedily become the subjects of pathological investigation. The colour of 

 the iris generally, but not invariably, resembles in shade that of the hair, and a 

 hazel or pale golden iris has been thought to be an index of colour-blindness. Of 

 the truth of this particular conclusion no proof has been given ; but it is certain 

 that the amount of dark pigment on the back of the iris (uvea), increases or dim- 



•AO cottieb Ethnology. Jiy John Beddoe, B.A., M.l>., If 



