After the child is born other causes come into operation. The mental incapacity may develope at a constitutional crisis, such as the time of the first or second dentition, or of puberty ; the amount of brain-power which had been previously sufficient for the wants of the economy failing to carry it through such critical periods of development. • Masturbation in these cases may be an important factor in determining the break-down. Again, accidental causes may come into operation in a child who had never shown symptoms of mental failure. Thus, he may become idiotic as a result of repeated convulsions or epileptic attacks, of chronic hydrocephalus, of injuries or blows upon the head, of some inflammatory condition occur ring as a complication of acute disease, and of impairment of the senses interfering with the development of the intellectual faculties.
One form of idiocycretinisna—is endemic in certain parts, although it may also occur sporadically.
Morbid Anatonzy.—In most cases of idiocy—in all in which the mental deficiency is congenital—the brain is small and often imperfectly developed as well. There may be great simplicity in the convolutions, approaching to the condition of the brain in the anthropoid apes ; there may be atrophy of the medulla oblongata, and asymmetry of the base of the brain ; ab sence of the corpora genicialata, the corpus callosum, or even, as was seen in a case recorded by Cruveilbier, the whole cerebellum ; the convolutions may be shrunken and the brain substance hardened. In other cases the child may be from birth the subject of chronic hydrocephalus. The brain is sometimes abnormally large, but may present no obvious change to the naked eye. Still, from the researches of Dr. M. Jastrowitz it seems that even in these cases careful microscopic examination may detect alterations in structure in the minute tissues of the brain, especially a persistence of anatomical elements which are normal in the embryo, but which ought to have passed into another form in the growing child.
Again, there may be cranial as well as cerebral abnormalities. The sutures and fontanelles may undergo premature coalescence ; and if there be no compensation by unusually slow ossification at the base, allowing of greater expansion in that region, the entire cranium is well proportioned but very small, and profound disturbance of the growth of the brain is the consequence. If, however, there be basic expansion, a special type of physiognomical and physical development, which Griesinger has described as the " Aztec " type, results. When the base of the cranium is shortened
by ossification, it is indicated to the eye by malformation of the face. We find the eyes widely separated, a prominent ridge to the nose, and high and prominent cheek-bones. There may be actual microcephalus, and the development of the pons and medulla is often affected. Usually, however, a certain compensation is found in extension of the skull in different di rections, producing many varieties in the shape of the cranium, and allow ing of more or less expansion of the brain in the upper regions.
different methods of classification of idiots have been proposed. There is the psychical classification of Esquirol, in which the idiot is arranged into three classes, to the degree of speech of which he is capable. The first class includes those who use merely words and short phrases. The second class consists of those who can articulate monosyllables or certain cries. To the third class are referred those who are capable of articulating neither words nor monosyllables.
Idiots may be also arranged into three classes according to the devel opment of nervous function. A first class exhibits nothing beyond the re 'flex movement known as excite-motor. In a second class the reflex acts are consensual or sensori-motor, including those of an ideo-motor or emotional character. In a third class we see manifest volition ; their ideas produce some intellectual operations and consequent will.
Another classification is that suggested by Dr. Langdon Down, accord ing to their resemblance to ethnological types—the Caucasian, Ethiopian, Malay, and Mongolian. Dr. Down has also proposed a good practical classification, based on etiology, into 1, Congenital ; 2, Developmental ; 3, Accidental.
The congenital group embraces all those cases where the signs of mental deficiency date from birth, and includes as subdivisions : a, Stru mous ; b, Microcephalic ; c, Maer °cephalic ; d, Hydrocephalic ; e, Eclampsic ; f, Epileptic ; g, Paralytic ; h, Choreic.
The developmental idiot is a child who is born with a fair amount of brain power, but who breaks down at one or another of the developmental crises—at the first or second dentition or at puberty. Such children lose the power of speech and their minds seem to give way at one of these evo lutional stages. The group includes. as subdivisions : a, Eclampsic ; b, Epileptic ; c. Choreic.