COLOUR-BLINDNESS. 
503 
Prevost considers it occurs on an average in one out of twenty 
persons; and Wartmann, whose investigations almost exhaust 
the subject, thinks this estimate is not exaggerated. M. 
Lubeck rejects this conclusion as unsound, from the observa- 
tions having been made in England and Germany, where blue 
is the prevailing colour of the eyes ; and it is a question with 
him whether it occurs so frequently in persons the mde.s-colour 
of whose eyes are black or hazel. In answer to this, it seems 
the great majority of cases examined by Wartmann had black 
irides. 
This consideration, however, cannot be of much importance 
beyond the physiological correspondence observable with the 
ophthalmoscope between the colour of the iris and the fundus 
of the eye, by the relative determination of the pigrmntum 
'nigrum * in persons of different complexions. In adapting 
the eye to varying intensities of light, the pupil (iris) of course 
acts a principal part as to the amount of visual rays received, 
but its changes cannot have much effect upon the varying 
intensities of the vibrations to which the supplementary phe- 
nomena of colours are ascribed. It is the intensity rather 
than the character of the light that the iris controls, and which 
remains the same whatever sensation ‘of colour is excited. It 
is different with regard to the influence which sex seems to 
exert, for on an analysis of upwards of two hundred cases, the 
proportion of males affected is no less than nine-tenths of the 
whole. Thus, it would appear that in this respect, the per- 
fection of vision, the ladies have greatly the advantage over 
the gentlemen. There is, however, an interesting account 
given by M. Cumer of a family of thirteen females (extending 
through five generations), all of whom were colour-blind. On 
the other hand. Dr. Bronner, of Paris, relates the case of a 
learned chemist, a German, whose two daughters were free 
from their father’s defect. The children of the eldest one 
were likewise unaffected, whereas three sons of the youngest 
were all colour-blind. A grandson, also, the son of one of 
these latter, inherited the defect. In the “American Journal 
of Medical Science,” 1854, another similar case is reported, 
where seventeen descendants, chiefly males, of the maternal 
grandfather all inherited colour-blindness. 
The two elder sons out of a family of four suffer from this 
defect. The second son, now an eminent sculptor, early in 
life exhibited great taste in drawing and painting, but after 
some few years of study was obliged to relinquish the art, in 
* I make no apology for introducing technical terms into this paper, since 
the anatomy of the eye is so well explained in a paper which appeared in the 
J anuary part of the present year. See page 220, 
