In accidental idiocy the mental break-down is the consequence of some shock or traumatic injury, or disease operating upon a healthy child born free from any tendency to intellectual deficiency. This group includes : a, Traumatic ; b, Inflammatory ; c, Epileptic.
Symptoms . —In cases of congenital idiocy the baby begins from an early age to show that he is not the same as other infants. The develop ment of his faculties does not run the ordinary course. He cannot support his head like another child, but lets it hang back on his nurse's arm. Then, he takes little notice. A healthy infant will often recognise his mother by the sixth week ; but long after that period the idiot child shows no recognition of faces. His eyes have a vacant look, seem incapable of fixing upon an object, and often oscillate from side to side (nystagmus). Again, he does not smile or laugh as a child will do whose mental develop ment is advancing naturally ; and manifests a strange inability to grasp with the hand. A healthy child's fingers curl round any object presented to them at a very early age, but the idiot infant seems to have no power of making any use of his hands. Moreover, when danced up and down, his muscles do not contract in sympathy with the movement. He seems to derive no pleasure from the exercise, but remains a dead weight like a heavy doll.
The head is usually noticed to be peculiar in shape from an early age. It is often high in the crown, and perhaps the fontanelles are closed, or nearly so, at the end of six months. Again, from the investigations of Dr. Langdon Down it appears that a high-vaulted palate—the V-shaped palate —with a very narrow transverse diameter is a common deformity of the congenital idiot. The tongue is often corrugated with transverse furrows, and sometimes is not completely under command. It hangs out of the mouth, and the child dribbles in an unusual degree even for a baby. The teeth are commonly late in being cut and often appear irregularly.
At twelve mouths old, when the child should be able to stand, or should at least crawl on the floor and try to raise himself on to his feet, he lies just as he is put down, without an attempt to move himself along. Often he does not learn to walk until he is three or four years old. It is also difficult to teach him cleanly habits, and he remains infantine in his ways at an age when other children have long been taught decency and order.
When idiocy is congenital, growth and development are impaired as well as mental power, and the general health is far from satisfactory. The patient is stunted in his stature and looks younger than his age. The cir culation is often feeble, and the temperature a degree or two lower than that of health. The feet are cold. The heart is frequently small and weak in structure, and there may be an open foramen ovale or other congenital deficiency. Often other malformations are seen, as imperfect development of one or more fingers, a club foot, or some strange shape of the ears.
Such children may show signs of rickets, and are not seldom of decidedly scrofulous constitution. As they grow up, an unpleasant smell is often noticed about the body and breath. In bad cases automatic movements are present ; chorea and epileptic fits are common complications, and the senses are frequently dull.
Griesinger describes two special varieties of idiots—the apathetic and the excited.
The apathetic class are awkward, clumsy, and disproportioned, with re pulsive, old-looking features. From their torpor and impassiveness they seem to be in a dreamy state. Their expression is either brooding and melancholy, or vacuous and indifferent.
The excited or agitated class are just as stupid as the other, but are quick in movement and irritable, passing rapidly from one impression to another, and quite incapable of fixing anything on their mind.
Between these two principal groups there are many intermediate va rieties.
There is one form of idiocy, endemic in some countries, sporadic in others, which merits a separate description. This is cretinism. The fee= bleness of intellect from which cretins suffer is combined with striking peculiarities of bodily structure. The condition is always congenital. It is not hereditary in the ordinary sense, although where the other conditions inducing the disease prevail, the child will become cretinous more certainly if born of cretinous parents. The disease has been said to be dependent upon the general causes of ill health—bad air, bad water, imperfect drain age, insufficient light and poor food, combined with the use of water loaded with calcareous salts. It may therefore prevail in any quarter of the world where these conditions are found; and certain close valleys in the Alps, Pyrenees, and Himalaya mountains are especially notorious for the number of cretins born in them. The value of these causes in produc ing the condition has, however, been called in question. Perhaps it is best to say that nothing positive is known with regard to the etiology of the dis ease. Whatever the cause may be, it appears to be also the cause of goitre, for cretinism and goitre are frequently associated. It has been said that act ing feebly the causes produce goitre, acting strongly they give rise to cre tinism ; but even this is hypothesis. Cretins are not invariably goitrous. In deed, in sporadic cases, such as occur from time to time in London, it is not uncommon to find that the thyroid body is absent. In two cases which came under my own notice no trace of a thyroid body could be detected. It is in places where cretinism is endemic that it is usually complicated with goitre ; but even in such neighbourhoods the goitre is not confined to cre tinous subjects ; and the area over which goitre is endemic is much larger than that in which cretinism is prevalent.