SCOPE OF GENETICS 45 



Mendelian analysis of these facts shows 

 that colour-blindness is due, not, as might 

 have been supposed, to the absence of some- 

 thing from the composition of the body, but 

 to the presence of something which affects 

 the sight. Just as nicotine-poisoning can 

 paralyse the colour sense, so may we conceive 

 the development of a secretion in the body 

 which has a similar action. The comparative 

 exemption of the woman must therefore mean 

 that there is in her a positive factor which 

 counteracts the colour-blindness factor, and 

 it is not improbable that the counteracting 

 element is no other than the femaleness- 

 factor itself. 



I think I have said enough to prove that 

 after all, those curiosities collected from ob- 

 servation of Sweet Peas and Canaries have 

 no remote bearing on some very fascinating 

 problems of human life. 



