LESS IMPORTANT HEREDITARY AFFECTIONS. 307 



It is to be noticed, that although only one of four- 

 teen sons of the third generation escaped, only one of 

 nine sons in the next generation was a bleeder. This 

 happy state of things was, in all probability, due to 

 reversion to the healthy type taking place in conse- 

 quence of intermarriage with healthy persons. 



All that need be said of this hereditary affection is, 

 that " women of ' bleeder ' families should certainly 

 not be permitted to marry." * 



COLOUR-BLINDNESS. This is another abnormal con- 

 dition which is in almost all cases hereditary, yet is 

 not, so far as has been ascertained, associated with or 

 allied to any other hereditarily transmitted abnormal 

 state. Like the hsemorrhagic diathesis, it is largely 

 confined to the male sex, though not so exclusively so 

 as that disorder. It is found in 3 to 5 per cent, of the 

 whole male population, but in only .2 per cent., or less, 

 of the female. 



This diseased condition, as its name implies, con- 

 sists of an inability to distinguish the various colours 

 one from another. Bed and green and other comple- 

 mentary colours are most commonly confused. Blind- 

 ness to all colours is rare, but in some few cases black 

 and white only are distinguishable. 



This insensibility to colour arises from an abnormal 

 condition of the retina, and that this is a degenerate 

 condition is, I think, proven by the fact that blindness 

 to colours, exactly as we find it in the congenital cases 

 at present under consideration, occurs in the earlier 

 * J. Wickham Legg, F.R.C.P., in "Quain's Diet, of Medicine." 



