AND ENVIRONMENT 23 



infection. Nowadays, 8 to 10% of people die of tuber- 

 culosis; perhaps another 3 to 5% are seriously incon- 

 venienced by it in one form or another. Is it mere 

 chance infection that this 10-15 % are selected from their 

 fellows ? Clearly the question of the prevalence of the 

 infection, and effective infection, is a fundamental in- 

 quiry. Yet you may look through the whole of Dr. 

 Newsholme's large and popular volume on phthisis and 

 find no real information on this all-important point. All 

 he does is to state, without inquiry, that / have none. 

 Now I find it a very useful precept never to make a 

 statement without a sohd ground of fact, but in most 

 pubhcations some statements will occur for which want of 

 space precludes full evidence. Your critics invariably 

 rush at these points — I suppose from a general experience 

 of how common vague statements are — and then they give 

 themselves away. It is a simple rule, and only involves 

 such self-control as is summed up in never speaking 

 without facts, but sometimes storing your facts. In this 

 case the facts were not mine ; they were the common 

 property of medical science, available to all those who 

 realize that medical literature is not confined to a few 

 English writers. For years the Germans have made 

 a special study of the prevalence of tuberculosis in 

 urban populations. There has been nothing nearly so 

 excellent done in this country nor, indeed, elsewhere. 

 At first, by careful post-mortem examinations, Hannau, 

 Schlenker, Burkhardt, and Nageli have shown that at 

 least 50% of adults who die from other causes have 

 suffered from latent or healed tuberculosis. Hamburger 

 and Sluka found that 47 % of all children between 11 and 

 14 showed healed tuberculosis, and that no less than 77 % 

 of children of the same ages showed some form of tuber- 

 culosis. Since nothing like 30 % die of tuberculosis, this 



