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whose names were on the register. The number of notifications received
in the district then will be swollen by a much bigger figure when a new
population moves into the district. These factors do not arise in stable
communities, but they are of much importance in developing districts.
(2) Register. The names of those who have been notified are
entered on a register which it is the duty of the medical officer of health
to keep up to date, by arranging for the removal of the names of those
who have died, or who have left the district. While the number on
an efficiently kept register is an index of the extent to which tuberculosis
occurs in the population, it is no true index of the influence of the district
in causing such disease, because of the inclusion of the names of those who
transferred into the district suffering from the disease. As the register is
dependent on the notifications of the disease, as such an index it is subject
to the same weaknesses as are the notification rates.
(3) Deaths. Most of those who suffer from tuberculosis die from
the disease after a longer or shorter interval. The death rate, then,
should be a reliable index ; but again it is not for a number of reasons.
If it is an index of anything it is of the volume of disease amongst the
population and not of the factors causing the disease. The length of time
a patient survives from the time the disease is notified depends partly on
its stage of development at that time. By mass radiography the disease
is detected in some much earlier than it would otherwise have been.
Not only are the chances of complete cure in such persons that much
greater, but if the disease should progress it will ordinarily be that much
longer before causing a fatal issue.
On the other hand the absence of facilities for treatment and the
length of time patients have to remain at home before they can be admitted
to hospital to start their treatment must have an effect on the development
of the disease. Such factors as these reduce the value of the death rates
from the disease as an index of the influence of living in the district on
its development, as must also such factors as the age and sex distribution
of the population.