38 



THE RELATIVE STRENGTH OF 



eye and eyelid, we appear to get a slightly more definite, but still a 

 quite negligible relation between disease and home environment. A 

 difficulty is whether to include strabismus or not ; the correlations 

 have been worked out by Miss E. M. Elderton, of the Eugenics 

 Laboratory, including and excluding "squint." In each a positive 

 correlation means that there is more eye disease with the worse home 

 condition. 



Feature of the Home Estimated 



Economic conditions ... 



Overcrowding 



Physical state of parents 

 Moral state of parents... 



Now, it is quite impossible to lay any stress on these results. Six 

 out of the 16 show less disease with worse home conditions, and if we 

 have positive correlations of o'lo and 0*14, we have negatives of 

 — o'lo and — o'i5. Further, no correlation of this kind lying under 

 about 0*25 can be really considered to have definite importance. How 

 very different these values are from the values running from 0*4 to o-6 

 found in our memoir for the inheritance factor! 



It is worth while putting on record here the quantitative contri- 

 butions of refraction and diseases of the eye in producing defective 

 vision. The refraction results are taken from our memoir ; the 

 disease results have been recently worked out by Miss Elderton. 



It will be seen that, if we exclude strabism.us, the diseases of eye 

 and eyelid do not produce half the effect on vision that refraction 

 does. 



