28 TUBERCULOSIS, HEREDITY 



period of quiescence or stability. Before 1847 the scanty 

 data available seem to indicate an extraordinarily rapid 

 fall in the phthisis death-rate. During our first period 

 from 1847 to 1866, instead of stabiHty we notice that the 

 death-rate from phthisis fell long before the general 

 death-rate, and before what I have ter ed the period 

 of sanitation. This in itself indicates a natural rather 

 than an artificial decay of phthisis. During the sanita- 

 tion period (1866-91) the fall in the phthisis death-rate 

 has been more marked than in the general death-rate, 

 and most noteworthy decreases took place. Now we 

 come to the last period involving three things (1891-1910) 

 — the discovery of the tubercle bacillus, the introduction 

 of sanatoria, and the so-called Fight against Tuberculosis. 

 Please regard my diagrams carefully here. To begin with, 

 they are made out without a knowledge of the census re- 

 turns for 191 1. What will be the effect of this knowledge 

 when it comes to us? Now it seems to me that of two 

 things we may be certain — (i) that the estimated popula- 

 tion will exceed its true value ; (ii) that the population in 

 actuality will be more adult than its estimated distri- 

 bution, — it will have more individuals in the phthisical 

 ages. Now what does this mean ? I think it must indi- 

 cate that the known number of phthisical deaths have 

 to be divided by a lessened exposed-to-risk population, 

 but that this will be slightly counteracted by the age 

 averages. In other words, our rates for the years 1900 

 to 1910 are almost certainly too small. I think we may 

 safely say that our curves do not exaggerate but mini- 

 mize what has been taking place, namely, that during 

 the years of tubercle bacillus, of sanatoria, and of the 

 fight against tuberculosis, the rate of fall in the death- 

 rate from phthisis, instead of being accelerated, has been 

 retarded. 



