The consistence of the brain is liable to increase under very different circumstances, and in every degree, from that which is imperceptible to that of a leather-like or fibro-cartiliginiform hardness and resistance. In the slighter degrees, there is no evident or decided anomaly, and it is most probable that they mainly depend on a diminution of the quantity of water in the brain; but in decided cases it arises from atrophy, shrinking, and change of structure. The more important indurations, therefore, must be classed among the diseases of the texture of the brain.

Induration is either total or partial: it affects the whole brain equally, or some single, larger or smaller, part of it only. The partial indurations are generally distinguished for the great degree of hardness they attain, and are known as a callous state or cicatrix of the brain.

The minor degrees of increased consistence, that, for instance, which is commonly selected for the study of the fibrous arrangement of the brain, are best marked after great and exhausting exudative processes, such as peritoneal exudations in puerperal women, or in the course of ileo-typhus, typhoid fever, and acute exanthemata, especially of scarlatina. And here, in opposition to Gluge, I must expressly state, that such a degree of condensation of the brain is the rule in typhus; while, on the other hand, decided softening, which, in fact, is nothing more than oedema of the brain, is certainly common later in the disease, in the train of evils connected with the disordered states of the system which follow typhus.

In poisoning by sulphuric acid (Otto), though I have had abundant experience, I have met with no instance in which the consistence of the brain was increased. In poisoning with lead, on the contrary (Andral, Tanquerel), though the consistence of the organ was sometimes increased, and, in a few cases, a high degree of it was combined with shrinking of the brain, there was much more commonly an unnatural softening resulting from oedema.

More advanced degrees of increased consistence, those in which the cerebral mass becomes tough like leather, accompany atrophies of the brain, as well those which are total, as, and more particularly, those which are partial. The most marked example of them is that which attends the partial atrophies resulting from a previous change of texture, apoplexy, or inflammation (p. 288). In such examples, circumscribed dense cicatrices are found in the parenchyma of the brain.

Induration in its highest degrees presents a fibrous, cartilaginous, or scirrhous hardness, and results from a serious disease of texture, especially from infiltration of the cerebral substance with cancerous matter. The disorganized portion of brain appears to have nearly or entirely lost its natural texture; and, in the latter case, the cerebral substance at length disappears in the foreign mass. (Compare "Cancer of the Brain.")