b. The same remark applies to the secondary softening. This form either immediately surrounds a spot of apoplexy or an adventitious product (in which case, as in the primary, it is entirely free from vascularity and reddening); or it skirts a spot of inflammation, or some inflamed cerebral substance which itself surrounds an apoplectic spot or adventitious product. The line of boundary between the inflammation and the softening is, however, sharply defined, and no injection or reddening extends beyond it into the region of the latter. It may even surround the rarer kind of dull white inflammation.

c. It does not contain those products and elementary formations which are usually found in inflammation.

d. The yellow color is certainly not dependent on the presence of pus and pus-cells; nor is the proper color of the fluid that of pus; it acquires its yellow puriform tint from being mixed with cerebral tissue.

The theory, therefore, which ascribes the origin of yellow softening to inflammation appears to be quite untenable.

Blood-corpuscles, and the pigment already alluded to, have as little to do with the production of the yellow color as purulent matter. Especial care must be taken not to commit the common error of confounding the color of yellow softening with the rusty-, yeast-, or ochre-yellow tints of the cerebral substance in cases of apoplexy and inflammation, which undoubtedly depend on the coloring matter of the blood. The color in yellow softening entirely differs from these; and, indeed, cannot arise solely from the coloring of the blood, for the fluid contains far too small a quantity of blood-corpuscles, as well as of the amorphous pigment, to account for it.

It is remarkable, that yellow softening of the brain never gives rise to any inflammatory reaction around it.

My own impression is, that yellow softening is founded in a chemico-pathological process.

As Couerbe's view, which was suggested by the equivalence in composition, or the isomerism, of the Eléencé'phol of the brain with another of its constituents, the Céphalote,1 - a view which was adopted by Ma-gendie, - must be rejected as a mere ingenious combination; so neither can Fremy's theory be accepted, which was drawn from the process of putrefaction in the brain. But it must be admitted that, whilst yellow softening does not exhibit the remotest similarity to the decomposition of the cerebral substance in the putrefactive process, much use may be made of Fremy's views, and that they have given a direction to future investigation which is full of promise.

1[See Magendie's Lécons Orales, t i. p. 159. - Ed].

He considers the brain to consist of cerebric acid, either free or combined with soda and phosphate of lime, of oleo-phosphoric acid, free and in combination with soda, of olein and margarin, of small quantities of oleic and margaric acids, of cholesterine, water, and a substance like white of egg, in the proportion of 7 parts of albumen, 5 of fatty matters, and 80 of water. The oleo-phosphoric acid, which, like the olein, is usually yellow, is very easily acted on (sehr veränderlich), and separates readily under slight influences into phosphoric acid and olein. Thus it decomposes at an ordinary temperature, when it comes into contact with water; and decomposing animal matters give rise to a similar change in it. Now, what first occurs in putrefaction of the brain is this decomposition of the oleo-phosphoric acid. But the process does not stop here; for the albuminous matter, also decomposing, sets up a further decomposition in the olein, and genuine saponification is the result - a conversion into oleic acid, and a combination of that acid with ammonia. Fremy thinks that this is the process which goes on in softening of the brain, - that it is, in fact, a genuine putrefaction of the brain. Although, as I have already said, I cannot discover any of the phenomena of putrefaction in the process of yellow softening, yet the liberation of an acid, - the phosphoric, and especially one or more of the fatty acids, - may be conjectured to be one of the most important phenomena in yellow softening. The conjecture is supported by the very decided acid reaction of the fluid contained in the softened spot.

A second question which arises has reference to the proximate palpable cause of the process. Considering how commonly yellow softening occurs both around a spot of inflammation, and in those portions of brain within it which are uninjured by the exudation, that it is also developed outside the halo of inflammation which surrounds apoplexy and morbid growths, and even immediately around these growths themselves, we may infer that obstruction of the vessels in the inflamed part, or impermeability of them from pressure, and the consequent impeding and interruption of the circulation in a portion of the brain, may be one considerable predisposing cause. And then, under certain circumstances, the contact of the cerebral tissue with extravasated blood in different stages of metamorphosis, and with the products of inflammation, might give the first impulse to the occurrence of yellow softening.

It appears, then, that yellow softening, and it alone of all the examples of softening of the brain, may be ranged side by side with softening of the stomach. In both of them alike, the possibility of any inflammatory reaction in the diseased tissue is absolutely precluded.