CXXV1II BOWMAN LECTURE. 



necessary by such terms as* '" partial" or "incomplete." 

 The problem for human Tn*e"cfical observers is, not whether 

 degrees of human albinism, either general or localised, 

 exist, but how far we may carry our subdivisions what 

 are the smallest tracts or lowest decrees of deficient pig- 

 mentation that may be intl^flej. an the species. It is, I 

 think, likely, although we cannot' -j^s yet either prove or 

 disprove the point, that pwpfafflt j&ibinism of any one part 

 does not occur without peiffe^t albinism of the whole body. 

 But as we have already 3ee2i f qjv the eye, and as is well 

 known also for the skin and-jjair/we find short of albinism 

 perfect dissimilar degrees & it in the same individual, 

 irregularities of distribution*, and differences in the same 

 tissue or organ at different periods of life. 



(b) DAY-BLINDNESS WITH TOTAL COLOUK-BLINDNESS. 



(Figs. 61 to 64.} 



This interesting but rare hereditary disease is always 

 accompanied by amblyopia, often of high degree, due to 

 defect at the centre of the field ; the f undus may appear 

 normal, or slight changes about the macular region and 

 at the disc may be present, not, however, such as would 

 lead one to expect any serious defect of sight. There is 

 always colour-blindness, and in the severer cases it is, as 

 the title indicates, total, but in some milder cases the 

 want of colour sense is less pronounced. No special kind 

 or degree of ametropia is found. Nystagmus is a usual 

 but not invariable symptom. The condition is always 

 said to date <( from birth/' and it gets neither worse nor 

 better with age. The patients almost always say they see 

 best in a dull light, and sometimes put it that they are 

 " blind " in bright daylight ; this, the ordinary condition 

 in toxic amblyopia, retrobulbar neuritis and central 

 retinal disease, is often much more strongly marked in 

 the condition I am describing. The disease often occurs 

 in several siblings, but has, I believe, not yet been seen in 

 parent and child; it is, however, known to have occurred 



