The inordinate increase and accumulation of the secretion of certain organs, as the mamma, testis, gall bladder, and kidney, pro duce a degree of hardness, sometimes equal to that of dense tumors, arising from the in compressibility of the fluids themselves, and the state of condensation of the walls of the organs in which they are accumulated.
Effusions of serum and blood into the tissues from mechanical causes produce great distension and induration ; such is the ease in the cedeina of the cellular tissue of the extremities in dropsy ; effusion of serum into the intermuscular cellular tissue produces hardening. Pulmonary apoplexy and ecchy mosis in various organs, from a mechanical impediment to the return of blood to the heart, have a like effect.
But inflammation of a sub-acute form is the great cause of induration, from the effu sion of serum and coagulable lymph ; the former of which is absorbed, and the latter becomes " induration matter," whose proper ties are described under the head of ADVENTI TIOUS PRODUCTS ; this last product produces induration on account of its being actually denser than the tissues into which it is effused, and, also, by its compressing power, for it has the peculiarity of contracting and becoming hard after its deposition. Certain morbid states of the blood, occasionally produce in durations of certain organs.
The changes of form, with which indura tion may be connected, are numerous ; none may, however, occur ; the bulk also of in durated structures varies ; it may remain un changed, but, generally, it is increased, and more rarely, decreased.
The colour of indurated parts, is generally different from the normal tint ; sometimes, owing to diminished vascularity, and to the presence of induration matter, it may be pale ; at others, owing to increased vascularity, and the state of the fluids of the tissue, and the presence of effused or infiltrated matters, it rnay be bright or dark red, grey, yellow, and sometimes almost black.
Induration presents several degrees of re sistance to pressure or to the knife ; much depends on the ordinary cohesion of the af fected organ. Generally speaking, the first degree is characterised by a slight increase in the resistance to pressure; the second finds the tissue denser, cutting with a cracking noise ; and the third comprehends increased cohesion, amounting to a cartilaginous or bony hardness.
Softening of the brain may be ascribed to inflammatory action, or to a defective state of the circulating apparatus of the organ • it rnay be an effect of a defective or perverted state of the body generally, and it is frequently caused by post mortem agencies. Now these four varieties of softening, although, as re gards their external appearances they have much in common, differ considerably from each other, each having peculiar attributes. The first and second varieties are generally found in the most, and the third in the least, vascular parts of the brain. Post mortem softening occurs, for the most part, in the immediate neighbourhood of the ventricles, is usually very diffused, is found on both sides at once, and is, of course, never preceded by symptoms.
Softening of the brain may be partial or general, and may present various degrees : the least change of consistence is only to be recognised by the microscope ; in a more ad vanced degree the softening is obvious to the unassisted senses, at first to the touch and then to the eye, the diseased part being pul taceous, and readily removed by a stream of water, a cavity surrounded by healthy struc ture being made evident.
In a more advanced degree still, the cere bral substance instead of being pultaceous is quite diffluent, and occasionally a perfect so lution of continuity is found. The softened portion of brain presents various alterations of colour. In inflammatory softening, the colour mainly depends upon the previous quantity of blood in the part; it may be of a deep red colour, with or without effused clots of blood, and frequently merges at the edges into at first a deep, and then a pale, yellow colour. Sometimes the yellow colour is central and the reddened portion external, resembling a collection of pus, so much so that Lallemand described it as such.
A dull red ochre colour with more or less hardening in the neighbouring structure, is indicative of chronic disease of long standing; as is also a chalky milk appearance, and a bright vermilion, of a recent effusion of blood into a previously softened part. In com mencing softening, a diffused blush, with or without spots of blood, is generally found. A deep grey colour and fawn and dirty white tints accompany' inflammatory softening, but much more frequently that which is produced by a deficient supply of blood.