nce of memory. This memory deposit facilitates the occurrence
of the chemical reaction constituting the memory along the same path
the next time. Forgetting then consists in a disappearance of these
memory traces or deposits. Forgetting is greatest in the first hour
after remembering, more than half of the memory trace being lost in
that time. Comparison of the curve of forgetting, and the curve
of diffusion of a colloid like gelatine from its solution, into a
surrounding medium, shows them to be exceedingly similar. Forgetting
may be explained by some such loss of the memory trace or deposit into
the blood continually flowing by it.

The internal secretions influence the amount and duration of the
memory deposits. The thyroid appears to be essential to the _laying
down_ of the memory trace. Cretins have poor memories on the retention
side and so cannot learn. The memory of thyroid insufficients is
wretched. In the extreme grades, the memory for recent occurrences
becomes completely lost. Iodine and thyroid increase the electric
conductivity of the brain, so that the memory trace must be deposited
more easily in those who have an excess of thyroid. Removal of the
thyroid produces a degeneration of nerve cells and their processes,
and associative memory becomes difficult or impossible because
conduction from cell to cell is interfered with. If sufficient thyroid
is fed in excess, brain conduction may be so facilitated that epilepsy
may result upon slight irritation.

On the other hand, the pituitary seems to be related to _preservation_
of the memory deposit. In conditions of disease of the pituitary,
loss of memory for past experiences is more marked. As regards recent
experiences, they are better held, although in a sort of subconscious
manner, recoverable when the condition improves or is cured. But the
greatest difference between the thyroid and pituitary effects upon
memory exists as regards material: the thyroid memory applies
particularly to perception and percepts, the pituitary to conception
(reading, studying, thinking) and concepts.

Judgment is another mental process that often intervenes between
sensation and the energy-reaction. It involves memory and association
of experiences. Behind it is an attitude as much as there is in an
emotion or the arousing of an instinct. Beliefs and reasonings are
complex judgments. They form the units of the intellectual process.

There is an element of speed in judgment