NURTURE AND NATURE 



class parents, but I suppose the argument to be that the children are kept more 

 at close work and that this damages their sight. Now, it would be possible to 

 compare the sight of children of the same age who came to school at different 

 ages originally, and thus find out whether those who began to read earlier have 

 markedly worse sight. It would be very desirable to collect statistics de novo 

 on this point. The only material that I know of bearing on the subject is that 

 used by Miss Harrington and myself, and provided by Cohn, who gives the 

 correlation tables of sight and years of school life, and sight and age. We have 

 shown that the relationship is more intimate between sight and age than between 

 sight and years of school life, and that, considering the high correlation of years 

 of school life and years of age, the latter is most probably only a derived result 

 of the former. Now, we have recently re-worked Cohn's data and discovered 

 the correlation between the ages at which the child began to read and the 

 degree of myopia at a constant age. The partial correlation coefficient is : 



0-04, if age and length of school life have a correlation of 0-8 

 0-13, if age and length of school life have a correlation of 0-9. 



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

 compare it with the heredity correlations of 0-40 to 0-60, and we see that 

 environment is quite overmastered by heredity. Furthermore, the correlation 

 has the wrong sense, 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 : 



Percentages of Corneal Nebula. 



1 This category should 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. 



