26 



111! K! .1. AII\i: STRENGTH OF 



Now it -. -.!.. nlniiirily difficult to lay any itmi ->n n Milts whose 



differences are of this order. A bad moral state of parents would be interpreted 

 to mean less comeal m-bula for the boys and more for tin- nirls. the percentages 

 being just reversed. Good economic conditions in both boys and girls would 

 mean 1-5 per cent, more of the disease, and so would the good physical 

 condition of the parmts. In such circumstances what stress can be laid on 

 the 0-8 per nut difference between crowded and non-crowded homes? The 

 only safe conclusion to be drawn is that in Edinburgh at least there is no 

 marked relationship between corneal nebula and bad home environment. The 

 curious point is that if we take all diseases of the 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 Ethel M. Klderron, of the 

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

 corr.-laticn means that there is more eye disease with the worse home condition. 



Percentages of all Eye Diseases. 



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

 the 16 show less disease with worse home conditions, and if we have positive 

 correlations of o-io and 0-14, we have negatives of - o-io and - 0-15. 

 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 0-6 found in our memoir for the inheritance 

 factor in eyesight ! 



It is worth while putting on record here the quantitative contributions 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 Ethel M. Elderton. 



