NURTURE AND NATURE 



37 



Now it will, perhaps, be said that the latter is a quite sensible 

 correlation, but compare it with the heredity correlation of 0*40 to 

 o'6o, and we see that environment is quite overmastered by heredity. 

 Fm'thermore^ the correlation is the wrong way^ the later the child 

 went to school^ the worse at a given age is the myopia. I have little 

 doubt that the correlation in this case is sensibly zero^ or the age at 

 starting reading has little influence on the result. Cohn's statistics 

 are, of course, not final, but they are very suggestive, because they 

 have hitherto been supposed to prove the exact reverse of what is 

 really extractable from them. 



I now turn to the question of the effect of good or bad home 

 environment on disease of the eye. I will consider first corneal 

 nebula and illustrate by some of the percentages : 



Now it is extraordinarily difficult to lay any stress on results 

 whose differences are of this order. A bad moral state of parents 

 would be interpreted to mean less corneal nebula for the boys and 

 more for the girls, 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 

 parents. In such circumstances what stress can be laid on the 

 0-8 per cent, difference between crowded and non-crowded homes 1 

 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 



^ This category should a priori be considered the most important one in 

 this matter. It marks essentially neglect of the children. Where the home is 

 practically a brothel or the parents habitual drunkards there can be no proper 

 cleanliness or care of offspring. 



