When the fluid begins to increase in the ventricles, these become dilated, as a rule equally, occasionally unequally, from obliteration of the foramen of Monro. The dilatation may be restricted to the lateral ventricles, or may include the third and fourth also. With the distention of the ventricles compression of the brain-substance takes place, giving rise to functional impairment of various kinds and degrees. With increase of pressure, atrophy of the compressed parts occurs. The septum between the ventricles may disappear and the brain-envelope become thin as paper, so that the hydrocephalus is like one enormous

Fig. 304.-Brain of a blind hemiplegic idiot. Atrophy and microgyria in both occipital lobes. (See history of case," Proc. N. Y. Path. Soc.," 1894, p. 98.)

cyst filling the cranial cavity. The basal ganglia and brain-stem become flattened. Examination of the cerebral envelope shows atrophy and degeneration of cells and fibers. The distention may go on until the cerebral tissues and the membranes vanish almost entirely. The amount of fluid has been known to reach six, eight, ten, twenty, and even twenty-seven pints. The following is an instance in point (a case from the Randall's Island Hospital for Idiots, the autopsy of which I reported at the New York Pathological Society. See "Proceedings," 1894, p. 94):

A female child, aged eighteen months; hydrocephalus, whether

congenital or acquired unascertained. Circumference of head, 51.5 cm. ; anteroposterior diameter, 18 cm. ; greatest transverse diameter, 15 cm. ; naso-occipital arc, 32 cm. ; binauricular arc, 34 cm.

Blindness and nystagmus; widely gaping fontanels; spastic diplegia; occasional convulsions, and just before death opisthotonos. At the autopsy sixty-four ounces of reddish serum were first removed by tapping the anterior fontanel. The skull and dura were exceedingly thin. The falx cerebri had disappeared. Cutting through the thin dura, nothing was to be seen of any brain proper in the great cavity of the head. The membranes usually covering the cerebrum had disappeared with that organ. At the base of the skull the floors of the ventricles and basal ganglia stood out prominently, and back of these parts, lying on the tentorium, were the only vestiges of a cerebrum

parts of the two occipital lobes. On removing the tentorium, the cerebellum was found to be of about normal size. Microscopical examination showed degeneration and atrophy of the lateral columns of the cord (Fig. 305).

In this case, then, we have to do with distention and atrophy of the encephalon pushed to its greatest extreme.

Case IV, in a series of autopsies by Bourneville, is a good illustration of the nature of the process of compression and atrophy. A girl, a complete idiot, died at the age of about two years. Five hundred grams of fluid were found in the brain-cavity, the brain-envelope having become merely a sac of varying thickness. For instance, in the right hemisphere, over the whole of the temporo-occipital region, the wall of cerebral substance was but a millimeter in thickness, and at one place here, near the fissure of Sylvius, the brain-substance was

absent altogether at a space of four centimeters in diameter, closed merely by a fine meningeal veil. In this case, then, the process of complete atrophy of the brain was arrested by death.

As the ventricular cavities dilate, pushing the brain-envelope with them, the skull-cavity is distended and the cranial bones are separated, made thinner, and expanded in area. The enlargement of the head is directly proportional to the youth of the patient. Cases beginning before or shortly after birth will present greater expansion of the cranial cavity than such as have a later origin. Sometimes some sutures give way and others become synostosed. Where sutures are separated Wormian bones often form, or a membranous connection is established between the cranial bones.

Occasionally, in these cases of primary hydrocephalus, the defects of brain-substance are not due to pressure-atrophy, but there is an associated condition of malformation or defect. Thus, in an autopsy of Bourneville's, on a girl about thirteen years of age, with congenital hydrocephalus, idiocy, and epilepsy, the hemispheres of the cerebellum were totally absent, the cerebellum being represented by the vermis, which was the size of a pigeon's egg. Perhaps such a defect is due to a pressure-atrophy beginning very early in fetal life.

As regards the pathology of secondary hydrocephalus, we possess more definite knowledge. In this the internal hydrocephalus is caused by obstruction of the veins of Galen, or by obliteration of the foramina of Monro, Magendie, or Mierzejewski. Common causes are tumors of the cerebellum, such as sarcomata and tubercles. Meningitis may act in the same way. The amount of hydrocephalus, ventricular dilatation, and expansion of the skull thus induced will depend directly upon the youth of the infant or child. As a rule, secondary hydrocephalus never reaches the extent of the primary form, owing to the rapidly fatal nature of its cause. In these cases we seldom see pressure effects beyond flattening of the convolutions and moderate expansion of the cranial vault.

An exceptional and an extremely interesting case was one upon whom I made an autopsy at Randall's Island, not long ago. It was a case of very marked hydrocephalus in a child of four years, in which a small tumor of the pineal gland, the size of a small hazel-nut, compressed and obliterated the aqueduct of Sylvius. Both of the lateral ventricles were enormously distended, the left more than the right, and contained twenty-four ounces of clear fluid. The third ventricle was also widely dilated. The fourth ventricle was of normal size. Microscopical sections of the quadrigeminal region revealed the obliteration of the aqueduct. The tumor was apparently tubercular, but was not examined, it having been mislaid and lost.

The cases of acute hydrocephalus due to meningitis serosa, and the cases in which a defect of brain-substance is counterbalanced by an equal bulk of cerebrospinal fluid, do not commonly fall under this heading.

In chronic hydrocephalus internus there seems to be a special susceptibility of the membranes to acute disease, so that at autopsy it is not uncommon to find evidence of an acute meningitis, simple, hemorrhagic, suppurative, or tubercular.

The fluid found in hydrocephalic idiots has been frequently analyzed. In a case of Bourneville's the analysis of the hydrocephalic fluid, withdrawn nine hours after death, resulted as follows: Color, pale yellow; aspect, clear after standing; reaction, neutral; odor, like that of blood; consistence, slightly viscous; density, 1.006; organic matter, 1.65; salts, 10; total fixed solids, 11.65; phosphoric acid, 0.22; sodium chlorid, 0.80; albumin, 0.26; leukocytes, very few; red blood-corpuscles, considerable.

In microcephalic idiocy we recognize three distinct classes:

1. Morphological microcephaly, in which there are no pathological changes in the brain, but simply a brain arrested in its development with persistent fetal morphology.

2. Pathological microcephaly, in which the small size of the head is determined by morbid processes in the brain (such as meningeal hemorrhage, thrombosis, porencephalic defects, etc.).

3. Mixed cases of microcephaly, in which pathological processes are superadded to or associated with true morphological microcephaly. The following table gives a summary of the pathological conditions responsible for most cases of idiocy :

In amaurotic idiocy but six autopsies have been made, and thus far the changes found may be considered to be simply degeneration of the gray matter of the cortex and of the anterior horns of the cord (Sachs).1

Diagnosis and Prognosis of Idiocy.-Diagnosis of Idiocy in General. It is seldom difficult to make a diagnosis of idiocy in childhood when the individual has reached such a stage of development that backwardness and deficiency stand out in prominent contrast to the normal average of intelligence in children of the same age. Occasionally, however, we have to deal with some species of insanity in childhood, in which case the matter of diagnosis is important because of the more favorable outlook for insanity. There are not a few pa

tients cared for in institutions for the feeble-minded and idiots in which insanity has been the original factor in the mental impairment, and when the histories of such are obscure, it is almost impossible to distinguish between ordinary idiocy and what may be truly termed a terminal dementia following upon some acute insanity of childhood. In these cases residual symptoms of a psychosis can be our only guide.

The diagnosis of some form of idiocy in infancy is far from easy unless one familiarizes himself thoroughly with the manifold steps of development for the first few years of existence. Early diagnosis is of the utmost importance, not only for the benefit of the unfortunate child itself, but on account of the deep solicitude of the parents for its future. One of the chief aids in differentiation will be found in a study of the physical condition of the infant. The shape and size of the head should be carefully noted and compared with normal shapes. and statistics. Unfortunately, there are no elaborate tables of head measurements in infants and children as yet made which can be looked upon as a final establishment of the normal averages, but the following figures are fairly representative of cranial measurements:

Malformation and asymmetry of the head should be taken into consideration. The various malformations are treated of in another chapter. The presence of marked anatomical stigmata of degeneration is of significance. Paralysis of a limb or limbs, if of cerebral origin, is of great importance, indicating, as it does, some lesion of the brain, which may retard or restrict mental development and lead to paralytic or epileptic idiocy, or both. Some of the morbid movements, such as nystagmus,

1"A Case of Amaurotic Family Idiocy with Autopsy," by Frederick Peterson, M. D.. "Jour. Nerv. and Ment. Dis.," July, 1898.