he
cities_, or, which is the same, with the number of proletarians. Extreme
hunger and want are less frequent in the country than in the city.

That the climate has an important influence on the appearance of
pulmonary consumption has long been known. In certain elevated regions
this disease seldom or never appears. This experience has been attained
in Switzerland and many other mountain regions. Furthermore the Plateaux
of Peru and Mexico are considered free from consumption, but also
lowlands like Iceland, the Kirgheez steppes and the interior of Egypt
are known to be exempt.

_Damp and windy climate_, especially with very high temperature, or
abrupt changes in the temperature promotes consumption; on the other
hand it is less frequent in the more moderated climates, especially if
they are dry.

Now when the tubercle bacilli have settled in the lungs, they cause
various symptoms. One of the most frequent is _cough_. In the beginning
of the disease a short, clear but light, very often dry cough appears.
During the further development of pulmonary consumption the cough
becomes more periodic; it appears early after awaking, in the afternoon
after dinner, and evenings at lying down; it may disappear entirely in
the meantime or may be light only; but then as a rule it is no longer
dry, but may be attended by expectorations of a varied nature.

[Illustration: Section of a tuberculous knot in the lungs, in which two
cavities are seen filled with numerous bacilli. The bacilli distinctly
appear as dark lines as a result of the coloring. Enlargement 900.]

[Illustration: Tubercle bacilli, Enlargement 2000.

To the left bacilli without spores, to the right bacilli with colorless
sections which are thought to be spores.]

The tubercle bacilli destroy the lung tissue and change it into pus,
which is coughed out. In this way larger and smaller cavities are formed
in the lungs; finally the cavities may even take more space than the
remaining lung tissue. When cavities have already been formed, coughing
comes easy and with abundant expectoration. Toward the end of life the
coughing and spitting stops as a result of the extreme feebleness and
weakness.

The violence and frequency of the cough depends mainly whether the
larger bronchial tubes and the trachea are affected; the more this is
the case, the more violent the inclination to cough. Further the
strength of the cough depends on the excitability of the patient; the
grea