muscles on the
side opposite to the lesion may first show spasmodic jerkings or
spasms (unilateral monospasm), and later the same groups become
paralysed (monoplegia). The paralysis frequently affects the whole of
one side of the body (hemiplegia) and the oculo-motor nerve is often
paralysed at the same time.

The pupils vary so widely in different cases that their condition does
not form a reliable diagnostic sign. Perhaps it is most common for the
pupil on the same side as the lesion to be contracted at first and
later to become fully dilated, while that on the opposite side remains
moderately dilated. As a rule, they are irresponsive to light.
Ophthalmoscopic examination shows swelling of the disc, and the
vessels of the papilla are distended and tortuous.

In cases which go on to a fatal termination, the coma deepens and the
muscular and sensory paralyses become general and complete. The vital
centres in the medulla oblongata gradually become involved, and death
results from paralysis of the respiratory centre. The fatal issue is
often hastened by the onset of hypostatic pneumonia. Not infrequently
a modified type of Cheyne-Stokes respiration is observed for some time
before death ensues.

A similar train of symptoms may ensue in cases of head injury as a
result of _pyogenic infection_ having given rise to meningitis or
abscess with accumulation of inflammatory exudate.

_Pathology._--When any addition is made to the bulk of matter inside
the cranial cavity, room is gained in the first instance by the
displacement into the vertebral canal of a certain amount of
cerebro-spinal fluid. The capacity of the spinal sheath, however, is
limited, and as soon as the tension oversteps a certain point, the
pressure comes to bear injuriously on the cerebral capillaries,
disturbing the circulation, and so interfering with the nutrition of
the brain tissue. As the intra-cranial tension still further
increases, the pressure gradually comes to affect the cerebral tissue
itself, and so the extreme symptoms of compression are produced. The
vagus and vaso-motor centres are irritated, and this causes slowing of
the pulse, contraction of the small arteries, and increase of the
arterial tension which tends to maintain an adequate circulation in
the vital centres in the medulla. The Cheyne-Stokes respiration is due
to rhythmical variations in the arterial tension: during the period of
fall the centres become anaemic and the respiratio