HISTOLOGICAL EXAMINATION OF AN ADULT HUMAN 
ALBINO'S EYEBALL, WITH A NOTE ON MESOBLASTIC 
PIGMENTATION IN FOETAL EYES. 
By C. H. usher, M.B., B.C., Camb. 
A. Introductory. 
When some ten years ago the subject of albinism was taken up by Karl 
Pearson, the late E. Nettleship and myself, the following problems naturally arose 
from the then state of our knowledge of the subject. 
(i) Is there or is there not a complete congenital absence of pigment in the 
eye of the albino ? This problem follows at once on the definition which had 
several times been repeated, that an albino was a person with complete congenital 
absence of pigment in the eye. The answer to this first problem could not be 
reached by clinical methods but only by microscopical examination of excised eyes. 
At the time just referred to not a single human eye had been reported upon which 
was entirely devoid of pigment. An examination of a portion of the iris only, 
even if it is found pigmentless, cannot be conclusive foi' settling the question of 
entire absence. 
(ii) l^he presence or absence of a fovea and of yellow colour at the iriacula 
in the case of the albinotic eye. Presence and absence of both have been asserted. 
But in some of the few available cases there is no evidence that a thorough 
microscopic examination of an adequate series of sections was made. 
(iii) What truth is there in the theory originally propounded by Meckel and 
Mansfeld, that the source of albinism is to be sought in an arrest of development ? 
Such a theory involves the extent of pigmentation in an albino corresponding to 
that of some foetal stage. Accordingly the study of the development of pig- 
mentation in the foetal eye becomes of very great interest. It would be of 
greater interest still, if we knew or could find out anything about the pigmentation 
in the eye of the albinotic foetus. 
The accompanying stTidy is a contribution of data bearing upon the above 
problems. It consists in the microscopic examination of an albinotic eye and of 
the eyes of normal dark-raced foetuses. 
