Any injury to the brain may destroy or seriously impair the
mentality of the individual. This is too well known to need
detailed exposition. Yet some cases of this type are fundamental
in the exquisite way they prove (if anything can be proven) the
dependence of mind upon bodily structure.

In some cases of fracture of the skull, a piece of bone pressing
upon the brain may profoundly alter memory, mood and character.
Removal of the piece of bone restores the mind to normality. This
is also true of brain tumor of certain types, for example,
frontal endotheliomata, where early removal of the growth
demonstrates first that a "physical" agent changes mind and
character, and second that a "physical" agent, such as the knife
of the surgeon, may act to reestablish mentality.

In cases of hydrocephalus (or water on the brain), where there is
an abnormal secretion of cerebro-spinal fluid acting to increase
the pressure on the brain, the simple expedient of withdrawing
the fluid by lumbar puncture brings about normal mental life. As
the fluid again collects, the mental life becomes cloudy, and the
character alters (irritability, depressed mood, changed purpose,
lowered will); another lumbar puncture and presto!--the
individual is for a time made over more completely than
conversion changes a sinner,--and more easily.

Take the case of the disease known as General Paresis, officially
called Dementia Paralytica. This disease is caused by syphilis
and is one of its late results. The pathological changes are
widespread throughout the brain but may at the onset be confined
mostly to the frontal lobes. The very first change may be--and