ible, if an
area of the skull is momentarily depressed by a localised blow, space
is provided for it by displacement of a quantity of cerebro-spinal
fluid, which sets up a fluid wave, and this by hydrostatic pressure
increases the tension of the fluid throughout the entire brain.
Vessels may be lacerated at any point, either by the flow of this wave
or during the ebb which follows the recoil. Hence it is that the
lesion is not always at the seat of impact, but may be at the opposite
side of the skull or at other remote points.

[Illustration: FIG. 184.--Contusion and Laceration of Brain. Note
limited lesion at point of impact on left side, and more extensive
damage at point of _contre-coup_ on right.

(After Sir Jonathan Hutchinson.)]

_Repair._--As the disintegrated brain matter is replaced by
cicatricial tissue, neither the nerve cells nor the fibres being
regenerated, the loss of function of the parts destroyed is usually
permanent. A localised extravasation of blood may become encapsulated,
and constitute a "haemorrhagic cyst." We have experimentally confirmed
Duret's observations and agree with his conclusions.

CLINICAL MANIFESTATIONS OF INJURIES TO THE BRAIN

For convenience, the clinical manifestations of cerebral injury are
usually described under the terms "concussion," "cerebral irritation,"
and "compression," but no precise pathological significance attaches
to these terms, they are essentially clinical. As the conditions so
described do not occur as independent entities and may overlap or
merge into one another their differentiation is more or less
arbitrary, and cases are frequently met with that do not run the
course characteristic of any of these groups.

#Concussion of the Brain or Cerebral Shock.#--The symptoms associated
with concussion of the brain are to all intents and purposes those of
surgical shock (Volume I., p. 250), the activity of the vital centres
being disturbed by violence acting directly upon the brain tissue
instead of by impulses transmitted to it by way of the afferent
nerves. Various theories have been put forward to account for the
depression of the vital functions in concussion. According to Duret,
with whose views we agree, the wave of cerebro-spinal fluid set in
motion by the impact of the blow on the skull, passes, both in the
ventricles and in the sub-arachnoid space, towards the base, where it
impinges upon the pons and medulla, stimulating the restiform bodies
and s