r 2 8 ANIMALS AT WORK AND PLAY 



colours by our brain, depends, not only on the 

 organ which makes the picture, but on the mind 

 which interprets it. It is largely the result of educa- 

 tion, even in those whose eyes are perfect, and who 

 are not colour-blind to any particular shade or tint. 

 It is possible that the animal eye, provided with all 

 the requisite apparatus for producing a coloured 

 picture, may be so ill-interpreted by the uneducated 

 animal brain that the creature sees mainly, though 

 probably not entirely, in monochrome. An evidence 

 of the latent and inert character of colour-vision is 

 that the human eye, which is trained to distinguish 

 colours, may also, by want of use, forget how to 

 distinguish colours. No human being would probably 

 be found so reckless of self in the pursuit of know- 

 ledge as voluntarily to submit to forego the use of 

 his eyes, and be blind for a season, to establish this 

 fact, that colour can be forgotten, as well as learnt, 

 by human sight. But the unique experience of 

 Dr George Harley, F.R.S., who, in order to save 

 the sight of one, perhaps of both eyes, when one 

 was injured, voluntarily immured himself in a room 

 made totally dark for nine months, shows that this 

 is the case. The fortitude which enabled him to 

 adopt this course, and the ingenuity by which he 

 preserved his health and faculties in this, the most 

 mentally and physically depressing of all forms of 



