The apparent transition from the precedi to this variety of polypus makes it probah that these also are new formations; and thoug they are sometimes firm and apparently fibro even when they are very small, yet perha they are often produced by the further dev lopement of the gelatinous variety. Mr. I kins says that, in general, when the p grows from the surface only of the m membrane it is soft and gelatinous; but whole thickness of the membrane, inclu also the periosteum, be its seat, or if it g• from a part where there is much fibrous as for example, near the posterior nares, fibrous; and this, no doubt, is generally tr yet the frequency with which portions of tl turbinated bones are pulled away in extracting gelatinous polypi proves that these also have often deep attachments.
What are called malignant polypi of the nose do not truly deserve the generic naine. They are cancerous diseases of the niucous membrane or of the parts situated on its ev terior, from which they gradually make their way into the nasal cavities. In general cha racters they do not dift'er from the similar dis eases of other parts. One form in which they appear is, that of common cancer of the mu cous membrane analogous to the hard or warty cancer of the skin, and pursuing the same course of apparently unresisted ulceration as that disease does. It occurs in old persons, and usually makes its progress very slowly, destroying all the adjacent parts till the patient is exhausted, or till it affects by its contiguity the brain, as in a case mentioned by Mr. Haw kins. The other chief form in which the nose is affected by malignant disease is that of the soft or medullary cancer ; but it is not certain whether this has yet been seen as a primary disease of the mucous membrane, or whether it be not always seated at first in some deeper tissue, from which as it makes its way it ac quires a covering from the mucous membrane, and appears to be truly a disease of the nose. Whichever it be, there is nothing peculiar in its characters or course to need a special descrip tion of it here.
NUTRITION.—The function thus designated may be regarded as including, in the most ex tended acceptation of the term, the whole series of operations, by which the alimentary Mate rials are converted into living organised tissue : but as many of these changes are separately treated of in other parts of this work, we shall here confine ourselves to a more limited range ; and shall consider the nutritive process as com mencing with the absorption of the materials, which have been prepared by the digestive pro cess; and as including all the changes, which are involved in the conversion of the fluids so intro duced within the system, into solid organised tissue, forming an integral part of the fabric.
The o/ject of the process of nutrition is the continual production of new tissue, either for the augmentation of the-original structure, or for the reparation of that part of it, which is continually undergoing decay or disintegration. And by this continual renewal of the/tissues, we gain, as will hereafter appear, a constant re invigoration of those vital powers or forces, the exercise of which has been one of the chief causes of the previous waste. It is a principle now generally acknowledged by physiologists, that the processes of disintegrition and decay, in any organ or tissue, are more rapid, in pro portion to the functional activity which it has been called on to manifest ;* and we find that the tendency to decomposition in the different tissues after death, which doubtless bears a general relation to their respective needs of re newal during life, is the greatest in those, whose vital powers are most remarkable—the ner vous and muscular tissues for instance ; whilst it is the least in those, whose properties are most purely physical—such as bone, cartilage, yellow elastic tissue, &c. Hence it is in the
former that the greatest activity of nutri tion is required, for the maintenance of their normal texture and properties; but its amount will vary, according to the demand created by previous activity, and the conse quent decay.
The materials required for the nutrition of the tissues of the animal body seem to be sup plied, for the most part at least, in forms pos sessing a similar chemical composition, by the vegetable kingdom. It will be presently shown that albumen may be regarded as the pabulum, at the expense of which all the organised tex tures (properly so called) of the animal fabric may be constructed. The really-organised part of this fabric, indeed, appears seldom to de part widely from the protein type of composi tion. Thus in fat, the non-azotized matter is contained within cells, whose walls are com posed of a protein priociple ; and in the ner vous tissue, it is probable that the walls of the cells and tubes are composed of an albuminous compound, though their interior is occupied by a substance of a character much more nearly approaching that of fat. Even with respect to the gelatinous tissues, as they are termed, there is much doubt to what extent they con tain gelatin in their normal state; for where this can only be extracted from them by long boiling, it is not improbable that an actual con version takes place ; since we know that pure fibrin may be converted, by long boiling, (which occasions the liberation of arnmonia,) into a compound resembling gelatin in many respects. And in those which are most purely gelatinous, it is doubtful how far the gelatin is itself organized. The writer has lately ex amined the sound of a cod with great care, both before and after the action of hot water upon it, and is satisfied that the gelatinous portion of it exhibits nothing that can be properly called organization—the only distinct appear ances of fibres, cells, &c., being presented by portions which were left undissolved by the hot water, and which were, therefore, to be regarded as more allied to albumen than to gelatin in their composition. Similar remarks may be made in regard to the horny substance depo sited in certain tissues ; and it may probably be stated as a general theorem, that whilst in the plant, the materials which it derives from the elements around are combined and elabo rated into non-azotized compounds for the pro duction of organized tissue, and into azotized products for deposition in its cavities, these last alone form the materials of the animal or ganisrn, any non-azotized substances contained in it being inorganic in their condition.