s made up of a
series of thin, interlacing, and branching _filaments_, some of which
are broken up so as to form masses or chains of _cocci_; and around the
periphery of the colony are elongated, pear-shaped, hyaline, _club-like
bodies_ (Fig. 30).

Infection is believed to be conveyed by the husks of cereals, especially
barley; and the organism has been found adhering to particles of grain
embedded in the tissues of animals suffering from the disease. In the
human subject there is often a history of exposure to infection from
such sources, and the disease is said to be most common during the
harvesting months.

Around each colony of actinomyces is a zone of granulation tissue in
which suppuration usually occurs, so that the fungus comes to lie in a
bath of greenish-yellow pus. As the process spreads these purulent foci
become confluent and form abscess cavities. When metastasis takes place,
as it occasionally does, the fungus is transmitted by the blood vessels,
as in pyaemia.

_Clinical features._--In man the disease may be met with in the skin,
the organisms gaining access through an abrasion, and spreading by the
formation of new nodules in the same way as tuberculosis.

The region of the mouth and jaws is one of the commonest sites of
surgical actinomycosis. Infection takes place, as a rule, along the side
of a carious tooth, and spreads to the lower jaw. A swelling is slowly
and insidiously developed, but when the loose connective tissue of the
neck becomes infiltrated, the spread is more rapid. The whole region
becomes infiltrated and swollen, and the skin ultimately gives way and
free suppuration occurs, resulting in the formation of sinuses. The
characteristic greenish-grey or yellow granules are seen in the pus, and
when examined microscopically reveal the colonies of actinomyces.

Less frequently the maxilla becomes affected, and the disease may spread
to the base of the skull and brain. The vertebrae may become involved by
infection taking place through the pharynx or oesophagus, and leading to
a condition simulating tuberculous disease of the spine. When it
implicates the intestinal canal and its accessory glands, the lungs,
pleura, and bronchial tubes, or the brain, the disease is not amenable
to surgical treatment.

_Differential Diagnosis._--The conditions likely to be mistaken for
surgical actinomycosis are sarcoma, tubercle, and syphilis. In the early
stages the differential diagnosis is exceedin