ocal focus of suppuration; by far the most
frequent cause is chronic suppuration in the middle ear. Less common
sources of infection are erysipelas of the face or scalp, infective
conditions of the mouth or nose, and diseases of the bones of the
skull.

The organisms may reach the affected sinus directly by continuity of
tissue, as, for instance, when the transverse (lateral) sinus becomes
infected from a focus of suppuration in the mastoid process spreading
through the bone to the sigmoid groove and involving the walls of the
vessel; or they may reach it by extension of thrombosis in a tributary
vein--for example, when the superior sagittal (longitudinal) sinus is
infected from an anthrax pustule of the lip, which has caused
thrombosis of the emissary vein that passes through the foramen caecum.

The pathological changes are the same as occur in the suppurative form
of thrombo-phlebitis in the peripheral veins (Volume I., p. 285). The
soft clot that forms adheres to the inflamed wall of the sinus, and,
being infected with pyogenic bacteria, it soon undergoes purulent
disintegration.

The infective process may spread backward along tributary vessels, and
so give rise to cerebral or cerebellar abscess, or to purulent
meningitis; or it may spread into the internal jugular vein and lead
to the development of a diffuse purulent cellulitis along its course.

General pyaemic infection may take place from pus or bacteria getting
into the circulation, either directly or by reversed flow through
tributary veins. Infective emboli are liable to lodge in the lung or
pleura, and set up pulmonary abscess, gangrene of the lung, or
empyema.

_Clinical Features._--In all cases, pain in the head, referred to the
region of the affected sinus, and so severe as to prevent sleep, is an
early and prominent feature. The patient is usually excited,
hypersensitive, and irritable in the early stages, and becomes dull
and even comatose towards the end. Rigors, followed by profuse
perspiration, occur early and increase in frequency as the disease
progresses. The temperature is markedly remittent, varying from 103 deg.
to 106 deg. F. (Fig. 196). The pulse is rapid, small, and thready. Loss of
appetite, vomiting, and diarrhoea are almost constant symptoms.

[Illustration: FIG. 196.--Chart of case of Sinus Phlebitis following
middle ear disease in a boy aet. 13.]

#Phlebitis of Individual Sinuses.#--The _transverse_ (_lateral_ or
_sigmoid sin