6 THE CAVENDISH LECTURE 



distinguish four things : (i) How far defective sight is a result of 

 parental defect. (2) How far it is affected by purely growth 

 changes. (3) How far it is a product of home habit and environ- 

 ment. (4) How far it is a product of school environment and 

 habit of posture, of type of books, and of lighting. 



Now what is the actual process? The bulk of " entrants " are 

 too young to have their eyes properly examined at all, certainly 

 not in the time allowed for it. You next examine them when 

 they are leaving school, and supposing you did make even 

 then a thorough examination, you could do but little for them, 

 because they are leaving school and you are losing touch with 

 them. And granting the sight is defective when they are twelve 

 or thirteen, how are you to tell whether it is due to school 

 environment, home environment, heredity or growth changes ? 

 You can only investigate these all-important points if you have 

 a large enough sample of children of all ages carefully observed, 

 and have studied them in association with their homes and 

 parents. 



I do not write without knowledge of the splendid work done 

 in following up defective children into their homes by many 

 school medical officers. I am in possession of many pedigrees 

 provided by such energetic investigators in cases of cataract, 

 albinism, Polydactyly and other marked pathological states. 

 But these very men will tell you that this type of inquiry, which 

 should be an essential part of their work, is directly discouraged, 

 and must be done, so to speak, outside hours and sub rosa. " Your 

 business," they are told, " is to provide a remedy, not to investigate 

 causes." Can you conceive a more fatuous position to take up ? 

 The school medical officer recognises a large amount of myopia, 

 he is to treat each individual case as it comes to his notice, but 

 he is not to strive towards that knowledge which alone would 

 enable him to cut at the root of the evil ! It is precisely the 

 same with carious teeth — you can do little when a child is entering 

 at five or six, you can do nothing when he is leaving your control at 

 twelve to fourteen. The intermediate history is unknown to you, 

 and many a problem which could be solved in a few years by a full 

 school inspection of a sample group of children — for example, 

 whether caries is hereditary in character, is due to special food, to 

 the character of the water supply or to any other form of nurture 

 — remains a matter of pure guesswork and individual opinion. 

 These difficulties, such as I have indicated in the case of eyes 



