In all these cases the vital solid is often the chief and the principal cause. The want of elasticity arises from water being poured into the cellular membrane instead of the usual halitus; the flaccidity and flexibility from previous debility. It is extremely doubtful whether the tender fibres of soft parts can be even broken, independent of previous disease, except in consequence of extreme violence, which is not our object; and the fra-gile vitreum attributed to cold has certainly no foundation, for the heat in the internal parts is uniform, and cold could not produce the effect without the previous destruction of life from its sedative power. If softness exist independent of these previous diseases, it must be attributed to the larger proportion of water, or a change in the chemical combination. A similar chemical change must take place in cases of rigidity, but with a diminished proportion of water. We shall therefore consider softness and rigidity as diseases independent of the distinctions just noticed.

When softness becomes a disease, the increased proportion of water, as we have said, arises often from debility a disease of the vital solid. With respect to the chemical change, the chief substance which attracts our attention in the composition of the soft parts is the Gelatin, q. v. We must add, however, to the remarks contained in this article, some later discoveries. The gelatine then differs from vegetable jellies, in consequence of the union with lymph, an animalized fluid, containing or consisting of nitrogen. This lymph is more copious in advanced life, and in the same proportion the animal gelatine is less soluble in water. In the earlier periods of existence this gelatine admits of the union with water, but not of the later; so that softness is the disease of the young, and rigidity of the old. But we find, from Parmentier and Deyeux, that diseases chiefly affect the gelatinous parts of the blood; so that this gelatine, in early life, from its affinity with water, and in the later period if not supplied in due proportion, or with the requisite qualities, produces the diseases of the simple solid referrible to diminished cohesion. In each view, therefore, these diseases arise from an excess of water, or rather from debility; and from opposite states, rigidity, the disease of old age, must be understood. In the latter state, also, many of the smaller vessels are obliterated; the coats of the larger, which remain, are more dense, and less irritable; the exhalations fewer: changes which contribute to increased rigidity.

The fleshy parts of animals experience the progressive changes chiefly from the gradual addition of lymph in a large proportion, of which the fibres seem to consist, as they are not very soluble in water, and appear to yield nitrogen copiously; for though Thouvenel obtained what he styled extractive matter from flesh, muscles probably differ from harder parts chiefly in consequence of their containing the blood. This animalized lymph is apparently that portion of the blood which separates in the fibrin. The cartilages are chiefly gelatinous.

Bones are only subject to softness and friability, which must in this case be distinguished from fragility, as it chiefly arises from an absorption of the bony matter. Bones are originally gelatinous; and in this jelly a calcareous phosphat gradually crystallizes in different forms, accordingto the shape of the bone. (See Bones). The gelatinous part assumes the form of membranes by the pressure of the bony fibres, and may be seen when the earthy salt is separated by solution in acids. The bones of the foetus are naturally soft and flexible. They continue so in a certain degree till their shape is gradually formed by the action of the muscles. The degree of softness unsuitable to the age is what constitutes disease. It arises from weakness, as in rickets, and from diseased fluids, as in scurvy, and occasionally in syphilis; and immediately depends, in a great measure, on a defective supply of the earthy salt. In rickets, debility of the digestive organs precedes the softness of the bones, and in scurvy the whole system is weakened. In syphilis the bones are perhaps eroded, and become friable rather than softened. They are, however, sometimes softened in cases of general debility, without any peculiar affection of the digestive organs, frequently from a sedentary life, and from confinement by a long chronic disease. This softness, which generally produces deformity, and in one instance rendered the pelvis so deformed as to require embryulcia, or the Caesarian section in a woman who had before born children of the usual size, does not produce the peculiar appearance of rickets, because it happens when the shape of the bones has been more perfectly established, as we shall see in that article.

Since, however, our attention has been more particularly turned to the changes in the lymph, we may be allowed to doubt whether the softness of young bones, or the friability of old ones, is wholly owing to the change in the bony matter. Each may be affected by a change in the state of the lymph, as already explained, and in part to the greater or less extent of the vascular system: to these views we may return under Rachitis, q. v.

Morbi solidi vivi. The solidum vivum, in the language of Gaubius, is the living portion of our bodies, or, in other words, the nervous system, in which we include, with Dr. Cullen, the brain, the spinal marrow, and the nerves either as sentient or moving organs. The distinction of every part of the nervous system is excitement by stimuli, not acrids only, but every thing generally understood as necessary to life, as food, drink, air, heat, and even volition. As the functions of the nervous system are those of sense and motion, their exercise may be affected by the state of either organ, the state of the brain, or of the nerves in their progress.

The diseases of sensation are in part influenced by the state of the media through which they are conveyed, as those of the skin, the humours of the eye, etc. These will, therefore, give the appearance of different degrees of sensibility, without any disease of the nerves. Different parts of the body differ also in sensibility. The experiments of Haller place the heart in the first rank, and, in succession, the stomach, the intestines, the diaphragm, and the muscles. These have, however, been disputed; but the controversy need not detain us. In the sound state he is not probably in error; but, when inflamed, membranes, and particularly nervous expansions, are by far more sensible than the heart or the muscles. Sensibility also differs in various ages, sexes, temperaments, and idiosyncracies; in pregnancy and child bed, as well as from habit. The state of mind has also a considerable effect on the sensibility; and sympathy, as well as association, often greatly increases it. Dr. Cullen has supposed that the state of the nervous fibril, or the fluid in the nerves, greatly influences the sensibility, and the opinion gains force from the peculiar irritable state of some constitutions, chiefly known by the name of hysterical habits, where the sensibility is considerable. The state of the fibre, as affected by the blood vessels, interspersed, has a similar effect. We have just mentioned the increased sensibility from inflammation, and the professor supposes that the fulness of these vessels gives a greater tension, with which he connects, with great probability, increased sensibility.