l8 TUBERCULOSIS, HEREDITY 



the production of tuberculosis, we should anticipate that 

 the relation as to phthisis between husband and wife 

 would be at least as intimate as between father and son. 

 By the time a son reaches the average age of onset 

 he is largely removed from close contact with his father, 

 but husband and wife are always together. Now in my 

 data we had only the particulars as to the parents of 

 phthisical children and as to their brothers and sisters. 

 You will notice that we need a fourfold table ; we need 

 the number of phthisical and non-phthisical children of 

 non-phthisical fathers and mothers. This datum can 

 be supplied if we estimate the number of individuals 

 in the community who suffer from phthisis at any time 

 of their life. We have further to make a correction 

 for the history of the phthisical families when com- 

 pleted. According to Dr. Thompson 50 per cent, of 

 a family with tubercle are ultimately tuberculous. I 

 have taken 33%, as actually observed in incomplete 

 famiHes, and the 50% observed by Dr. Thompson in 

 completed families as the two ends of my scale. I have 

 also considered the difference in result which arises 

 from supposing first 10% and then 13% of the com- 

 munity—not to die, but to suffer at some time from 

 tuberculosis. The general conclusion is that the resem- 

 blance between parents and offspring lies between 0-40 

 and o-6o. Dr. Goring was more fortunate than I was. 

 His data actually provide the number of tuberculous 

 persons in his population, and the only corrections he 

 had to make were for completion of family history. 

 This he did in three different ways— (i) by including 

 only those individuals over 14 years, and then by 

 including only those over 23 years, and again, (ii) by 

 taking 33 %, and (iii) 50 % to be ultimately tuberculous. 



