52 THE FAMILY AND THE NATION 



statistical investigation by Pope and Pearson has shown 

 that such transmission is comparatively rare too rare 

 to affect appreciably statistical results. The disease is 

 so prevalent that no one can escape coming within its 

 influence. In crowded urban populations, at any rate, 

 we may safely assign escape or infection in a large 

 measure to immunity or predisposition. 



To reach definite conclusions on the intensity of 

 hereditary transmission, a careful statistical inquiry, 

 based on processes the same as those used to investigate 

 the inheritance of physical qualities such as stature, etc., 

 must be undertaken. Professor Pearson has found by 

 such methods that the coefficient of correlation for 

 the hereditary transmission of tuberculosis lies between 

 0.4 and 0.6, and has a most probable value of about 

 0.5 identical with the coefficient for the transmission 

 of physical dimensions. 



Other points of interest also appear. Among them 

 may be mentioned the fact that tuberculosis is more 

 prevalent among the older children of a tuberculous 

 parent than among the younger children. Similar 

 results are found in other pathological inquiries ; the 

 elder children are more liable to inherit the weak points 

 of their parents. The bearing of this tendency on the 

 effect of the decrease in the average size of modern 

 families is obvious, and full of sinister import to the 

 future of the race. 



One of the fundamental problems in sociology is the 

 determination of the comparative influence of heredity 

 and environment in the production of any given char- 

 acter. In most cases data for the examination of the 

 problem are wholly wanting. No figures, for instance, 



