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all its forms. It is a well-known fact that the sensibility 

 of the eye to light is very different in different persons. It 

 may vary as much as 200 per cent, and, of course, will pass 

 through all the intermediate degrees. Heredity transmits 

 these inequalities, from partial to total anaesthesia, or blind- 

 ness, when the eye, incapable of noting form or colour, has 

 only an indistinct perception of light. Congenital blindness 

 may run in families. Blind persons will sometimes beget 

 blind children. . . . Amaurosis, nyctalopia, and cataract 

 in the parents may become blindness in the children ; and 

 such transformations of heredity are not rare in animals." 

 Daltonism, or colour-blindness, is well-known to be heredi- 

 tary, and an example is quoted by Darwin, wherein in eight 

 families, akin to each other, this affection lasted through 

 five generations, and extended to seventy-two individuals. 

 Hyperaesthesia of the optic nerve frequently produces, in 

 some persons, great acuteness of vision, so extraordinary, 

 indeed, as to be almost regarded as supernatural. Several 

 examples of this are recorded by Prosper Lucas, in all of 

 which there was a potent hereditary element. As with all 

 other specific characters, in every species of animals, heredity 

 preserves and transmits a visual apparatus of a structure and 

 optical power peculiar to each ; so that there can alone be 

 any doubt with regard to individual varieties, but there are 

 good reasons for believing these also to be transmissible. 



Although it would be useless to institute an inquiry as to 

 which of the senses is the most important, since opinions 

 would inevitably differ, yet I cannot be far wrong in asserting 

 that that of hearing is of prime importance, since on it 

 depends not only the possibility of speech and, therefore, 

 thought, but it constitutes the foundation of the science of 

 acoustics, and also of the art of music. Similarly to sight, 



