OR COLOUR BLINDNESS. 173 
in detail. I shall confine myself to the citation of one of them 
entire, adding another which has been communicated to me. 
The most interesting case which I have studied is that of M. 
Louis D * **, born at Locle, July 22nd, 1810. He is the eldest 
of seven brothers and four sisters. His parents have a normal 
sight, and their children are assorted in a very singular two- 
fold category. The first is formed of those who have red hair 
and who are not daltonians ; the second, of whom D * * * is one, 
is composed of those whose hair is blond and whose vision is 
anomalous as to colour: each sex has representatives in each of 
these two divisions. 
D *** attests, according to his own recollection and the evi- 
dence of his mother, that in his infancy he perceived colours in 
the ordinary manner. Put to boarding-school at a very early 
age in the Canton of Berne, he returned at the end of two years 
without very distinct notions of their diversity, and thus reached 
his ninth year. He at that time received a hard blow on his 
head, so violent that the skull was fractured; the treatment 
of the wound rendered surgical operations necessary, some of 
them on the back, after which his perception of colours be- 
came defective. The fact, however, that three of his brothers 
are similarly affected, without having been placed in the same 
circumstances, takes from this pathological observation a great 
part of its importance. 
His father endeavoured, by repeated corporal punishment, to 
put a stop to what he called a perverse pretence, and D * ** re- 
members the correction which his master, a bookbinder, one 
day inflicted on him for having used red paper for some books 
the cover of which should have been green. 
I have subjected this daltonian to a great number of experi- 
ments, varied so that they should mutually check one another. 
I had, in fact, to guard against errors arising from faulty indi- 
cations on his part, and attributable to the education which his 
habitual relations compulsively give him. Moreover he did not 
disguise his repugnance to reply to precise questions on points 
where the absence of the perceptive faculty involves, as is known, 
that of the corresponding ideas, which no external process of 
instruction can supply the place of. 
D *** does not perceive any great difference between the co- 
lour of the leaf and that of the ripe fruit of the cherry; he con- 
founds that of a paper sea-green with the scarlet of a riband 
