Such a condition of the brain may, in the first place, be a consequence of some fault in its original development. The whole brain is then small, but the cerebrum is evidently the most diminished, and its convolutions may not be discernible (microcephalus, - congenital idiocy). Or it is some smaller portion, one of the pairs of cerebral organs, for instance, the development of which, in mass and volume, has been arrested: the anterior or posterior lobes of the cerebrum, on one side or both, the whole cerebellum, or one of its hemispheres, etc, may be thus diminutive.

But far more frequently, the small size of the brain is acquired at a different period of life. It consists then of an arrest of the development of the brain in bulk, in consequence either of premature closure of the sutures of the skull, or of the pressure of the fluid in meningeal hydrocephalus, or of various similar local impediments from without, or else of others, such as dropsy of the ventricles, which operate from within. Sometimes it consists of atrophy of a brain already fully developed. I proceed to a special notice of the last.

Atrophy Of The Brain

I may remark, in passing, that the same causes which have been mentioned as interfering with the development of the brain, such as chronic hydrocephalus, or local pressure, may occasionally produce atrophy, either of the whole or of part of it, and proceed to the consideration of the more important instances of atrophy, those which are primary and idiopathic, and those which are consecutive and secondary.

Idiopathic primary atrophy is an affection almost peculiar to old age, and is, within certain limits, a natural process of shrinking or decay (involution) of the organ (Atrophia cerebri senilis, - Senium cerebri). It becomes, however, a pathological condition, even in old age, if it proceed to a very great extent; and still more, if it come on prematurely at an earlier period of life. (Senium - marasmus cerebri prsecox).

This atrophy is confined to the cerebrum. Cazauvielh asserts that the cerebellum retains the full size in the aged, which it had reached in the younger person, at the completion of growth. In contrast, however, with the local, or partial atrophy, - that of separate parts of the brain, - it may be regarded as a total atrophy, or atrophy of the whole brain.

The cerebrum is diminished in volume and weight. The former is ascertained from the existence of a new space between the surface of the cerebrum and the skull, and from the enlargement of the ventricles.

The convolutions are thinner than natural, and the sulci between them broader. The gray substance is of a dirty, or rusty-brown color, running into yeast-yellow. Its consistence may be normal, or distinctly softer than natural. The fibrous substance has lost its pure whiteness, and has a dirty white tinge; it is denser, too, than natural, and is sometimes as tough as leather. This increase of density (sclerosis) is most marked near the ventricles. The ventricles are dilated, their lining membrane is generally palpably thickened, and is frequently covered with a very fine granular, gritty layer, of a crystalline transparency, or an opaque whiteness (p. 272).

More advanced degrees of atrophy and concomitant induration present the following appearance: The surface of a section of the hemispheres shrinks and becomes concave; and, here and there, certain portions offer more resistance than others, and wrinkle and lie in folds: sometimes these firmer portions surround the orifices of the vessels divided in the various sections, and the tissue around the end of the vessel shrinks, and encircles it with a little hard puckered projection.

The fibrous arrangement of the pons, crura, and similar white structures, is rendered more distinct than usual by superficial grooves running in the direction of the fibres.

The porous condition of the white structure of the hemispheres, and of the corpora striata, called by Durand-Fardel "état criblé is also very well marked. It is equally the result of the atrophy of the brain, and of the congestion of the cerebral vessels to which the atrophy gives rise; it consists of an enlargement of the canals in which those vessels traverse the brain.

The vacuum within the skull, produced by the shrinking of the brain, is filled up chiefly by a clear colorless serum, which accumulates in the sac of the arachnoid around the brain, in the tissue of the pia mater, and in the ventricles. For the same reason, the vessels of the pia mater become varicose, the membranes of the brain increase in volume, and bone is even deposited on the inner table of the skull, especially around the anterior cerebral lobes within the frontal bone.

This form of atrophy, as I have already remarked, occurs in old age; but it may also come on prematurely, and be associated, or not, with manifest senility of the entire organism. When thus premature, it sometimes arises spontaneously; but it is more frequently met with as a consequence of mental diseases which are characterized by excitement, and as the physical cause of the imbecility which follows them. It is one of the results of repeated intoxication and attacks of delirium tremens; and it ensues upon repeated attacks of apoplexy, especially peripheral apoplexy, and upon the processes by which they are cured. Inflammation, too, will bring it on, especially that which is peripheral and its termination in induration, etc.

It is in itself a very important condition, but it becomes still more so from its immediate and further consequences. Those consequences are as follow: