=Softening.= To be able to recognize readily any change in the consistency of the brain, clear ideas must first be had of the normal density of this organ. This may be obtained from an examination of the brain of some of the lower animals—as the sheep or ox—that has been killed in a state of health. We shall then find that the brain presents sufficient firmness to permit of its being handled without rupture of its substance, and to allow of its being sliced into thin sections which will support their own weight. The gray portion is somewhat softer than the white, yet the fibrous character of the latter, becomes apparent only after hardening in alcohol. If put into pure water, it continues unchanged for eight or ten hours, and without any portion becoming dissolved, or rendering the water any degree turbid. The consistence of the brain varies, normally, at different periods of life. In the fœtus and at birth, its softness approaches to semi-fluidity. From this to the fifteenth or twentieth year, it gradually acquires the firmness of the brain of the adult. =Softening=, one of the most common variations from the normal condition, is generally a mere result of inflammation of a chronic or sub-acute form, accompanied with a fatty degeneration of nerve substance. Under the microscope, the change is seen to consist in a disintegration of the nerve fibres, the medullary substance breaking up into large masses, and undergoing fatty metamorphosis. It may take place either on the _external surface_ of the organ, or in the _septum lucidum_ and _fornix_, the _corpora striata_, or _optic thalami_ of the ventricle, the central parts of the _hemispheres_, the _cerebellum_, or the _crura cerebri_, in the order mentioned. While this change is usually the result of inflammation, as already mentioned, it may accompany or succeed the following morbid conditions of the organ: 1. It may be the result of congestion of the vessels of some portion of the brain. In this case, the softened portion is reddish, crimson, or brown in color. 2. It may follow the effusion of blood in apoplexy. The softened portion is then of a brownish color, or, if considerable time has elapsed, it may be of a dirty ash color, tending to green. 3. It may accompany or follow the process which terminates in serous effusions. It is then of a milky-white color. 4. It may take place in the brain substance immediately around tumors, when its color may present a variety of tints. Among the causes tending to induce this condition of the brain, may be mentioned a diseased state of its blood vessels, or their obstruction by fibrinous clots; constitutional syphilis; excessive mental labor, or frequently repeated epileptic convulsions. The consistency will be found to vary from a slight change from the normal condition, to that of a soft, pulpy, or even cream-like condition.