6 TUBERCULOSIS, HEREDITY 



only be legitimate if I were basing percentages on many 

 hundreds— but I use them only to emphasize the nature 

 of the problems which arise, i. e. : 



(a) We have to inquire whether persons living habi- 

 tually in the same environment and with practically the 



III 



IV. 





•>4 *2 



9^0^ '9 (^AA 



VI IVJ Z#3#4#5#6 



I 1 1 1 T-^ 1 1 1 



vii .6 li 3i?46 s6 66 7f 8f?99 



Fig. III. Family Phthisis : Pearson's Case. 



same risk of infection have the same chance of develop- 

 ing phthisis whatever be their stock. There is no closer 

 relation than that of husband and wife. Is the mate of 

 a phthisical person as likely to acquire the disease as 

 the offspring of such a person ? 

 (b) If we find numerous cases of phthisis in a stock. 



