AND ENVIRONMENT 7 



does the disease reappear in the members who have 

 had no contact with the phthisical members ? or again, 

 do we find it skipping generations ? 



These problems are not easy problems to answer ; ^ 

 they are surrounded with very subtle statistical diffi- 

 culties, but I have no patience with those writers who, 

 without entering into any analysis of such pedigrees as 

 I have shown you, dismiss them with the remark that 

 they only represent ' family infection '. Do we meet 

 with risk of infection only in the family ? If not, what 

 is the relative importance of the risks we run within 

 the family and outside it? All these are problems 

 which want a thorough thrashing out, but which have 

 been largely side-tracked by the idea that infection is 

 the only factor worthy of our consideration. On these 

 topics I can only touch briefly to-night, but I should like 

 to bring some remarkable points to your notice. 



In association with the Biometric Laboratory much 

 statistical work has recently been done on phthisis. In 

 the first place we have tried to appreciate the extent of 

 marital infection in tuberculosis. 



From the family records in the Laboratory, if we leave 

 out the 0-5% of cases in which the condition of either 

 husband or wife was unknown, and add to the tuber- 

 culous the 0-6 % of cases returned as doubtful, we have 

 on the basis of 1,000 marriages in the professional classes 

 the results shown in Table I. This indicates that in 

 1,000 marriages there are 55 wives and 49 husbands 

 tuberculous, and of these 6 cases of tuberculous hus- 



^ The work of Dr. Chalmers in Glasgow is undoubtedly on the right lines, 

 but as represented in the Reports of the Local Government Board for 

 Scotland on the Administrative Control of Pulmonary Phthisis in Glasgow, 

 191 1, the necessary information just at the critical points appears to be 

 omitted. 



