The most prominent feature of softening of the brain, or encephalomalacia, is the alteration of consistence: but the disease results from other fundamental changes, and is treated of amongst the diseases of texture only for want of a more suitable place. Our previous investigation of certain examples of softening will have prepared us for the consideration of the whole subject, and we shall now, with regard to them, be referring only to what has been already asserted.

Notwithstanding the labors of many older and more recent observers, the anatomical diagnosis of softening of the brain is far from being either clear or complete. Without doubt, this deficiency has principally arisen from their neglecting to distinguish accurately the several forms of the disease. And it has been needed also that observations should be extended to analogous processes in other organs, especially to inflammation, and to that softening, disruption, and solution of tissue which characterizes inflammation wherever it occurs, as well as to its terminations in other structures also. Moreover, the disease has, from want of material, been insufficiently observed in its several stages; and, lastly, a lack of special observations supported by chemistry, especially of observations on yellow softening, has contributed to the same result.

Softening of the brain occurs under such totally different forms that it cannot be treated of as one general disease. For the same reason it is impossible to decide the question, whether it be of inflammatory nature, that is, produced by inflammation or not; a question which is answered in the affirmative by one large party, and in the negative by another equally large.

There are three essentially different forms of softening of the brain: two of them have been already spoken of; but, in order to complete the account of the disease, they must be again brought forward.

a. The first form is that which is met with in hydrocephalus (p. 269), and oedema of the brain (p. 304), as white, or hydrocephalic softening.

It consists in a loosening and subsequent laceration of the cerebral texture by an interstitial exudation of serum. Like oedema in general-it sometimes takes place without any inflammation, at other times it is unquestionably so far inflammatory that a certain quantity of a coagula-ble blastema, capable of assuming an elementary organization, is poured out with the serum. Examples of it are furnished in the more or less acute forms of oedema, which occur in the neighborhood of spots of inflammation, and more especially in the oedema which accompanies acute meningitic hydrocephalus, and destroys the tissues around the ventricles of the brain. In such cases of softening, the characteristic products of inflammation may generally be discovered with the microscope in the diffluent cerebral mass.

It does not appear to me necessary to suppose (with Paterson), that the brain is naturally hygrometric, in order to explain the occurrence of such a softening in the neighborhood of the ventricles, in cases of acute hydrocephalus; I have made frequent experiments, but have never found imbibition to produce a softening of the cerebral tissue, in any way resembling that which takes place in hydrocephalus.

Nor can I adopt Fremy's view (which will be taken into consideration, together with the subject of yellow softening). For white softening has, apparently at least, no connection whatever with putrefaction, and it is certain that it often exists for a long period as chronic oedema of the brain, and yet the serum is found to have caused no maceration or decomposition of the cerebral substance.

It is quite different from yellow softening, and has no analogy whatever with the process of softening in the stomach.

Its essential character, viz., that of destroying the cohesion of the brain, was recognized by Laennec.

b. The second form is that which has been described in the article on Inflammation, as red softening (p. 307), and in some few cases as a softening, marked by dull white discoloration (p. 308). There can be no doubt of its Inflammatory nature: and in the trifling amount of the discoloration, i. e. the whiteness of the softened tissue, the latter variety shows its alliance to inflammatory oedema. The softening results from the cerebral tissue being broken asunder and dissolved by the exudation.

This class includes, moreover, that condition which has been described (p. 310) as a termination of inflammation of the brain, as the termination in atrophy or absorption, or the so-called cellular infiltration.

All these softenings are found, as has been noticed in the separate descriptions of them, not only as primary and substantive, but also as secondary and symptomatic.

c. The third form is the yellow softening, which has hitherto been only occasionally mentioned. It is on every account a remarkable disease of the brain, and yet, singularly enough, it has received but little attention from observers until very recently, and is only cursorily mentioned by them: it is, however, the instance of softening that best supports the numerous opinions of German and French physicians who oppose the theory of its being of an inflammatory nature, especially those opinions according to which it is a disease sui generis, a specific alteration of nutrition, etc.

Yellow softening, like inflammation, never attacks the whole brain at once, but occurs as a primary and idiopathic disease in pretty sharply circumscribed spots.

At a spot which may vary in size, but which is scarcely ever larger than a hen's egg, the cerebral substance appears converted into a very moist, tremulous pulp, of the yellow color of straw, or sulphur, and not unlike brine (sulzeahnlich): when cut across it rises considerably above the level of the section; and it presents to the naked eye no trace of natural cerebral structure. The transition from the diseased to healthy structure is somewhat abrupt, passing through a thin layer of cerebral substance in which the disease is less advanced; the texture of the brain immediately around is found to be comparatively normal.