View report page

109
Bacilli are killed by exposure to direct sunlight, by the usual disinfectants, and by boiling:
but survive outside the body for long periods in conditions of damp, dirt, and bad ventilation.
Promiscuous spitting, especially inside buildings or vehicles, may be a particularly potent
source of infection: for the sputum of a consumptive is often heavily laden with virulent
micro-organisms, which are liberated into the surrounding air as the former dries up.
Predisposing factors.
Modern investigation has disproved the hereditary theory of tuberculosis—in other words,
it is not handed down as an unwelcome legacy from parents to children: though there may exist
in some families a disposition or weakness towards the disease.
The subject is thus bound up with the fact of infection—almost universal in civilised
communities—and a bodily resistance in the individual, which is sufficient to overcome the
invasion by tubercle bacilli in the great majority of persons.
This resistance, however, is largely influenced by other factors, and one can broadly state
that any circumstance which tends to lower bodily health at the same time lowers resistance to
disease.
Illness, excessive fatigue, anxiety states, toxaemic conditions or prolonged fevers all tend
tc- lower vitality, and therefore lower resistance to tuberculosis, giving rise to a particular state
in the individual that favours the multiplication of micro-organisms which may gain entry.
In 1933 there was conducted (under the auspices of the National Association for the
Prevention of Tuberculosis) an extensive investigation into the causal factors of tuberculosis in
two large industrial areas in the north of England—these two areas showing a particularly high
tuberculosis incidence and mortality rate.
The result of this enquiry was of the greatest importance as it showed that poverty, leading
to under-nourishmenit and over-crowding, was a marked feature in both areas.
Under-nourishment (especially in essentials such as fresh milk and fats) lowers bodily vitality
and hence resistance: whilst over-crowding with all its accompanying faults of defective hygiene,
lack of fresh air, and other insanitary conditions, favours the chances for continuous and perhaps
heavy infection.
Certain trades which involve the inhalation of special forms of mineral dust are characterized
by a peculiar condition of the lung tissue (known as librosis) due to continuous irritation:
and this is often complicated by infective processes such as tuberculosis.
In the female subject, pregnancy and prolonged lactation may sufficiently lower resistance
in certain cases, so that tubercular infection already implanted may become activated.
There are certain other factors, racial, sociological and climatic, which have been considered
to have a bearing on this subject, but are largely a matter of controversy and space forbids any
discussion on them.
Historical.
Proof of the cxisitence of tuberculosis can be traced back to remote antiquity, for evidences
of its ravages have been seen in mummies from Egyptian tombs.