=Synonyms.=—Amentia; feeble-mindedness.
There are three grades of amentia:
=1. Morons:= those whose mental age corresponds closely to their
chronological age or is nearly normal.
=2. Imbeciles:= those in whom there is a wide disparity between the
mental age and the chronological age.
=3. Idiots:= the lowest form of arrested mentality or those whom it is
impossible to teach.
=Definition.=—Mental deficiency is a pathological stage in which the
mind has failed to attain normal development.
=Various degrees of intelligence= or mental capacity in man lie between:
(=1=) =Genius= such as Bacon, Newton, Plato, Galileo, Shakespeare.
(=2=) =Lesser Ability= but still conspicuous in development such as our
great leaders in science, literature, reform and the arts and medicine,
furthering, each their respective causes. These merge easily into
(=3=) =Average= mass of mankind.
(=4=) =Dullards= or those of inferior intelligence.
(=5=) =Feeble minded=, merging imperceptibly into
(=6=) =Imbeciles= and by insensible gradation into
(=7=) =Idiots= and gross idiots.
The mentally defective is wholly incapable at maturity of adapting
himself to his environment or local conditions in order to maintain
existence independent of any external support.
=Dementia= is a disease of the mind or that which was once possessed,
and by some neuronic disturbance is lost totally or partially.
=Insanity= is a disturbance of neuronic function which may or may not
end in degeneration of brain tissue.
=Physiology.=—The normal brain begins its development shortly after
fertilization of the germ cell, by the expansion of the anterior end of
the rudimentary spinal cord into four primary cerebral vesicles. These
develop into a series of elaborate infoldings, each with multiple cells
around them. At or about the sixth month of fetal life this embryonic
brain assumes the shape of the adult brain, minus the secondary
fissures and convolutions which are characteristic of full development.
At birth there are sometimes many convolutions and the brain weighs
from 280 to 330 grams. Growth is then rapid and at six months it weighs
from 560 to 680 grams;