CHAPTER VIII
TUBERCULOSIS
Tubercle bacillus--Methods of infection--Inherited and acquired
predisposition--Relationship of tuberculosis to injury--Human and
bovine tuberculosis--Action of the bacillus upon the
tissues--Tuberculous granulation tissue--Natural cure--Recrudescence
of the disease--THE TUBERCULOUS ABSCESS--Contents and wall of the
abscess--Tuberculous sinuses.
Tuberculosis occurs more frequently in some situations than in others; it is common, for example, in lymph glands, in bones and joints, in the peritoneum, the intestine, the kidney, prostate and testis, and in the skin and subcutaneous cellular tissue; it is seldom met with in the breast or in muscles, and it rarely affects the ovary, the pancreas, the parotid, or the thyreoid.
_Tubercle bacilli_ vary widely in their virulence, and they are more
tenacious of life than the common pyogenic bacteria. In a dry state, for
example, they can retain their vitality for months; and they can also
survive immersion in water for prolonged periods. They resist the action
of the products of putrefaction for a considerable time, and are not
destroyed by digestive processes in the stomach and intestine. They may
be killed in a few minutes by boiling, or by exposure to steam under
pressure, or by immersion for less than a minute in 1 in 20 carbolic
lotion.
Methods of Infection.#--In marked contrast to what obtains in the
infective diseases that have already been described, tuberculosis rarely
results from the _infection of a wound_. In exceptional instances, however, this does occur, and in illustration of the fact may be cited the case of a servant who cut her finger with a broken spittoon containing the sputum of her consumptive master; the wound subsequently showed evidence of tuberculous infection, which ultimately spread up along the lymph vessels of the arm. Pathologists, too, whose hands, before the days of rubber gloves, were frequently exposed to the contact of tuberculous tissues and pus, were liable to suffer from a form of tuberculosis of the skin of the finger, known as _anatomical tubercle_. Slight wounds of the feet in children who go about barefoot in towns sometimes become infected with tubercle. Operation wounds made with instruments contaminated with tuberculous material have also been known to become infected. It is highly probable that the common form of tuberculosis of the skin known as "lupus" arises by direct infection from without.
[Illustration: FIG. 33.--Tubercle Bacilli in caseous material
x 1000 diam. Z. Neilsen stain.]
In the vast majority of cases the tubercle bacillus gains entrance to
the body by way of the mucous surfaces, the organisms being either
inhaled or swallowed; those inhaled are mostly derived from the human
subject, those swallowed, from cattle. Bacilli, whether inhaled or
swallowed, are especially apt to lodge about the pharynx and pass to the
pharyngeal lymphoid tissue and tonsils, and by way of the lymph vessels
to the glands. The glands most frequently infected in this way are the
cervical glands, and those within the cavity of the chest--particularly
the bronchial glands at the root of the lung. From these, infection
extends at any later period in life to the bones, joints, and internal
organs.
There is reason to believe that the organisms may lie in a dormant
condition for an indefinite period in these glands, and only become
active long afterwards, when some depression of the patient's health
produces conditions which favour their growth. When the organisms become
active in this way, the tuberculous tissue undergoes softening and
disintegration, and the infective material, by bursting into an adjacent
vein, may enter the blood-stream, in which it is carried to distant
parts of the body. In this way a _general tuberculosis_ may be set up, or localised foci of tuberculosis may develop in the tissues in which the organisms lodge. Many tuberculous patients are to be regarded as possessing in their bronchial glands, or elsewhere, an internal store of bacilli, to which the disease for which advice is sought owes its origin, and from which similar outbreaks of tuberculosis may originate in the future.