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Page 40
From the lungs the bacilli are carried by the lymphatics to the lymph
nodes at the root of the lungs, in which a similar process takes
place; this, on the whole, is favorable, because further extension by
this route is for a time blocked. The extension by means of surfaces
continues, the abundant sputum which is formed in the lungs and which
contains large numbers of bacilli, becomes the vehicle of
transportation. The windpipe and larynx may become infected, the back
parts of each are more closely in contact with the sputum and are the
parts most generally infected. A large part of the sputum is swallowed
and infection of the intestine takes place, the lesions taking the
form of large ulcers. From the intestinal ulcers there is further
extension by means of the lymphatics, to the large lymph nodes in the
back of the abdominal cavity (Fig. 8-25); the bacilli may also pass
from the ulcers into the abdominal cavity and be distributed over the
surface of the peritoneum resulting in tuberculous peritonitis. When
the disease has reached an advanced stage, bacilli in small numbers
continually pass into the blood and are distributed by this over the
body, producing small nodules in many places. In rare cases
distribution by the blood is the principal method of extension, and
immense numbers of small foci of disease are produced, the form of
disease being known as acute miliary tuberculosis. Although the
bacilli are distributed everywhere, certain organs, as the brain and
muscles, are usually exempt, because in these the conditions are not
favorable to further growth of the bacilli. Tuberculosis, although
frequently a very acute disease, is usually one of the best types of a
chronic disease and may last for many years. The chronic form is
characterized by periods of slow or rapid advance when conditions
arise in the body favorable for the growth of the bacilli, and periods
when the disease is checked and quiescent, the defensive forces of the
body having gained the upper hand. Often the intervention of some
other disease so weakens the defences of the body that the bacilli
again find their opportunity. Thus typhoid fever, scarlet fever and
other diseases may be followed by a rapidly fatal advance of the
tuberculosis, starting from some old and quiescent focus of the
disease.
Tuberculosis is also one of the best examples of what is known as
latent infection. In this the infectious organisms enter the body and
produce primary lesions in which the organisms persist but do not
extend owing to their being enclosed in a dense and resistant tissue,
or to the production of a local immunity to their action. Dr. Head has
recently examined the children of households in which there was open
tuberculosis in some member of the household. By open tuberculosis is
understood a case from which bacilli are being discharged. He found
with scarcely an exception that all the children in such families
showed evidences of infection. The detection of slight degrees of
tuberculous infection is now made easy by certain skin reactions on
inoculation of the skin with a substance derived from the tubercle
bacilli. Such latent infections may never become active and in the
majority of cases do not. When, however, in consequence of some
intercurrent disease or conditions of malnutrition the general
defences of the body become weakened extension follows. Such latent
infections explain the enormous frequency of tuberculosis in prisons.
Under the general prison conditions infection in the prisons probably
does not take place to any extent, and the disease is as common when
the prisoners are kept in individual cells as in common prisons. It is
probable that in these cases the prisoners have latent tuberculosis
when entering, and the disease becomes active under the moral and
physical depression which prison life entails.
For the extension of infection from one individual to another the
infecting organisms must in some way be transferred. The most
important of the conditions influencing this are the localization of
the disease and the character of the infectious organisms,
particularly with regard to their resistance to the conditions met
with outside of the body. The seat of disease influences the discharge
of organisms; thus, if the disease involve any of the surfaces the
organisms become mingled with the secretions of the surface and are
discharged with these. If the seat of disease be in the lungs, the
throat or the mouth, the sputum forms the medium of extension, which
can take place in many ways. The sputum may become dried, forms part
of the dust and the organisms enter with the inspired air. The
organisms which cause most of the diseases in which the sputum becomes
infectious are quickly destroyed by conditions in the open, such as
the sunlight and drying; street dust does not play so prominent a part
in extension as is generally supposed. Organisms find much more
favorable conditions within houses. It is now generally recognized
that infection with tuberculosis does not take place in the open, but
in houses in which the bacilli on being discharged are not destroyed.
The hands, the clothing and surroundings even with the exercise of the
greatest care may become soiled with the saliva.
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