1910-11.] Incidence of Mortality from Pulmonary Tuberculosis. 365 
lungs among females in Scotland as compared to that in England and Wales 
must have operated during more than forty years (Table II.) both in urban 
and in rural areas (Plates III. and V., Tables Y. and VI.), the effect being most 
marked in the age periods up to 35-45 years (Table III.). The reduction in 
Scotland at all ages has been practically the same among males and females,, 
but between age periods 5-10 and 25-35 years it was less among females 
until 1901-5, since when it has been the same in both sexes. In England and 
Wales, while the reduction in female mortality at all ages has been much 
greater than in male mortality, the reduction among females has been the 
same as or greater than among males from age period 15-20 years onwards 
(Plate II.). Between the ages 5 and 20 years the phthisis mortality both in 
England and in Scotland, alike in urban and rural districts, has always 
been greater than among males. Leaving this point for later discussion, 
it remains that some influence has been at work in Scotland which has 
retarded the reduction of female mortality at age period 15-20 to 30-35 
years as compared to that among females in England and Wales, and among* 
males in both countries. 
In the etiology of tuberculosis of the lungs two factors are generally 
recognised, the bacillus and the condition of the body into which it enters, 
the relative importance of these being estimated differently by different 
authorities. The cause of the greater mortality among females in Scotland 
than in England and Wales may be either a greater exposure to infection 
or diminished resisting power among the female population of Scotland, 
especially at the early age periods, or to both of these. Any light on this 
point is most important in connection with the success of preventive measures. 
Fortunately many measures, such as improved housing, improved conditions 
in factories and workshops, school hygiene, etc., tend both to lessen risk 
of infection and to increase the bodily resistance. If the chief cause be 
greater exposure to infection, measures must be directed specially against 
the bacillus ; if diminished resistance of the body be also of great importance, 
then success will lie to a large extent in measures for securing general con- 
ditions of healthy living. 
Greater Risk of Infection in Scotland . — If this be the explanation, then 
it does not apply in the case of males, as their mortality has decreased rather 
more in Scotland than in England, and markedly so in the urban area 
since 1891-1900 (Tables I. and VIII.). Women admittedly spend a larger 
part of their lives in the dwelling than men, but probably this is not more 
the case in Scotland than in England. It is difficult to compare the housing 
conditions of the two countries. In the insular rural districts of Scotland, 
where the housing is as a rule far from satisfactory, and where the women 
