THE HUMAN COLOUR SENSE. 173 



Discussion. 



At the request of the Chairman, the author added some verbal 

 explanations of his diagrams, and a hearty vote of thanks was 

 accorded to him. 



Mr. D. Howard, D.L., etc. — 1 do not know whether the learned 

 author of this paper has considered the relation of this theory 

 (which I confess is extremely interesting, and one which commends 

 itself very much to my mind) to the question of colour-blindness, 

 which is one of the oddest phenomena that we have experience 

 of. Of course, the limitation of one's ear to sound is pretty 

 familiar to many people. I do not know whether you have 

 noticed how raany people are stone-deaf to a bat. I am, for 

 instance, but I think, on the other hand, I can hear a 50-foot 

 organ-pipe better than most people. A colour-blind person may 

 be utterly unable to see these two colours, and may be able to see 

 these two colours ^pointing on the diagrani]. What condition of 

 the nerves one can imagine to explain that is certainly difficult to 

 make out. Even with the idea of three nerves in each of the 

 cones, or filaments, whichever it may be, according to one's 

 imagination, it is very difficult to see how you get two out of 

 four colours] missing, and the other two perfect. It so happens 

 that T have known a good deal about colour-blindness since I was 

 a small boy. A school-fellow of m.ine, now my brother-in-law, 

 was absolutely colour-blind in red and green ; therefore my boyish 

 mind was taken up a good deal with it. A colour-blind woraan is 

 one of the rarest things possible, but here you have, undoubtedly, 

 relations of vibrations with colour, though the cause is difficult 

 to discover. 



Mr. HuLME, F.R.C.S. — Has Dr. Macdonald, in his experience, 

 found out what is the deficiency in colour in colour-blindness ? 



Dr, Macdonald. — -A normal deficiency occurs in the retina, 

 beyond a certain cone, tbat limit being confined to blue and yellow. 

 Outside a certain cone there are certain properties in the retina 

 itself which vary in perceptive power. 



Mr. HuLME. — It has fallen to my experience, as a surgeon to 

 the Marine Society, to examine boys, and I have never found (out 

 of the three colours on a table, red, violet, and green) a boy 

 refuse violet, and very rarely red. It is invariably the green. 



