i6 



TUBERCULOSIS, HEREDITY 



I collected over 220 cases of families and determined 

 in which stocks cases of phthisis had occurred, and in 

 which they had not ; in every case the husband and wife, 

 whether phthisical or not, were themselves omitted from 

 consideration. Table VIII is the result. 



TABLE VIII. INTERMARRIAGE OF TUBERCULOUS STOCKS. 

 Actual: Husband^ s Stock 



Coryelation 

 030 



Wife's Stock 



Chance : 



Wif^s Stock 



Transfer 

 + 3T I -31 

 -31 I +31 



In other words, 62 stocks are transferred and the corre- 

 lation is 0-30, as high as in the extreme case of mating 

 with regard to phthisis. Now it is clear that neither hus- 

 band nor wife was known to be phthisical at the time of 

 marriage, and yet in the middle and professional classes 

 phthisical stock tends to mate with its like. We are almost 

 forced to the conclusion that the occasions in which we 

 find husband and wife both phthisical are not — although 

 exceeding the range of chance — due solely to infection. 

 It seems probable that a very large proportion of what 

 is itself not very large is due to assortative mating. Now 

 many persons suspect all figures, and I have often heard 

 such a statement made as ' But if you had taken any two 



