The anomalous occurrence of fat is no less frequent than multiform. The subject is daily acquiring fresh interest, in proportion as the importance of fat in the animal economy, from the incipient stage of digestion through every process of assimilation, up to the formation of the elementary cell, renders itself more and more apparent. It is, however, quite within the compass of pathological anatomy to testify that protein substances, and in particular fibrin and albumen, are capable of undergoing conversion into fat.

Fat-Textures

1. Normal

We have already adverted to the excessive formation of fat generally, and to its accidental unequable accumulation about certain organs, amid general wasting of this tissue, for example, in the omentum, the kidneys, the mediastina, on the pericardium, and on the heart. We have here to advert more particularly to fat collections still more marked by their locality and limitation. Of this kind are -

(a.) Those collections of fat important in various ways, which encircle diseased, and especially calculous kidneys, or such as have become atrophied through Bright's disease, or surrounding anomalous bone-formations (offering some analogy with the medullary system of bone), as in ossifying arteries, in the vicinity of cancers, etc.

(b.) Lipoma or fatty tumor, an accumulation of adipose tissue in the shape of a spherical, oval, lenticular, more or less lobulated tumor, invested with a delicate capsule of areolar tissue, and permeated by equally delicate and spare continuations of the latter. Its size is from that of a hemp-seed or a pea, to that of a man's head, or more.

It consists, as a mere repetition of the normal adipose tissue, of spherical fat-cells, wherein are discoverable stellate or radiating crystals of margarine or margaric acid. Where the areolar tissue capsule is more strongly developed, the lipoma is an encysted one. We have met with such encysted portions in the midst of loosely lobulated lipomata.

The lipoma occurs chiefly in the subcutaneous areolar tissue, more especially in localities where fat is deposited in more than ordinary amount in the healthy state, and where accidental circumstances cause its still further accumulation, as at the glutaei, at the thighs, at the back and neck, about the shoulder. It is, however, also observed in parts less abounding in fat, as beneath the hairy scalp. Again, it occurs in the submucous areolar tissue of the stomach, of the intestine, even of the bronchia; in the subserous areolar tissue of the parietal, as well as of the visceral layer, although more commonly of the parietal, in serous and synovial sacs; for example, beneath the pleura and peritoneum, upon the inner surface of the dura mater, and upon the investing membrane of the ventricles. It has been fully described as it occurs in synovial sacs, more especially of the knee-joint, in that peculiar form which Joh. Muller has denominated lipoma arborescens; a form to which all lipoma-tous accumulations beneath serous sacs incline. We have also met with lipomata in glandular organs, more especially in the lungs, liver, and kidneys, in bone affected with osteoporosis and eccentrical atrophy.

Large lipomata in subcutaneous and in submucous areolar tissue, by dint of traction, acquire a pedicle, and lapse into the cavity, it may be of the intestine, in the semblance of a polypus.

Lipomata occur, for the most part, solitarily. Instances are not quite rare, however, of several, or even many coexisting beneath the subcutaneous areolar tissue. Such cases are the more remarkable, that they may affect individuals not otherwise at all prone to excessive fat formation.

In itself lipoma is innocent. By compression, traction, and hampering of space, it may be rendered nocuous. Moreover, its general integument may, through violent tension, through inflammation and suppuration, or through a sloughing process, occasion consecutive ulceration of the tumor, and exhaustion of the powers of life.

It is seldom traceable to palpable mechanical injury. In the majority of cases, more especially where several lipomata concur or succeed each other in growth, there is evidence of neither blow nor compression.

The term steatoma, so often misapplied of old, has been reserved by Johannes Muller to designate a peculiar species of lipoma, in which the fat texture is lobulated, as it were, through the intervention of a permeating membrane of areolar tissue, the latter forming a main constituent of the new growth, and imparting to it greater toughness.