The occurrence of free fat, - a condition, we think, properly meriting the term of fatty disease - takes place under different circumstances:

1. It is immediately secreted as such. The seat of its deposition are normal textures and their elementary parts, or else pathological growths.

To the former category belong:

[a.) Tallowy infiltration of the liver, a condition in the one instance resulting from spirit drinking; in the other, being the concomitant of tuberculous disease. In the former case it is often associated with a stearine-like character of the contents of the adipose tissue.

(b.) To the other mode of occurrence belong more especially the fatty contents of encysted tumors.

These fats differ in character. Thus, in ordinary fatty liver it is a normal fat, for the most part rich in elain, - in some varieties of fatty liver, the waxy liver, a more consistent fat, containing stearine and cholesterine.

In various cysts, again, we meet with a fat consisting in different proportions of elain, margaric, stearine-like fat and butyrine. Some cysts contain cholesterine alone; the majority, other ingredients besides. In this mode of its occurrence, fat is very generally associated with epider-moidal and with osseous formation.

2. Fat, as such, is liberated owing to new combinations taking place amongst the ultimate constituents of a complex formation. Or, again, it is not set free as pre-existent fat, but is newly created, and this out of protein substances, by dint of an elementary transforming power.

This transformation or metamorphosis into fat is rendered highly probable, if not certain:

(a.) By the large proportion of fat found at various epochs in the place of parts, into whose composition fat assuredly did not originally enter in anything approaching to its subsequent amount.

(b.) By this appearance of excess of fat occurring under conditions which preclude its derivation from a vascular system. It takes place in growths destitute of bloodvessels and often remote from vascularized organs; for example, in exudates, shut up within thick shrivelled sacs unfurnished with bloodvessels, - in stratiform deposits within arteries. It is even very commonly met with at the centre of the said formations, and therefore at the greatest distance from vascularized parts; as, for instance, in the coagula, within the vascular system, in tubercule-granules, and in crude fibre in circumscript masses.

(c.) Lastly, by the appearance of fats in the said formations being the forerunner of their entire metamorphosis, and generally speaking of their destruction.

For this adventitious production of fat, more especially as it affects a blastema in the progress of development, or even perfected textures, we find the term fatty disease or degeneration, peculiarly appropriate; and we consider it to be fraught with quite enough of interest for general pathology, to justify an attempt to enumerate here the various phases of its occurrence.

1. Appearance of fat in the blood [or fibrin] coagula in veins, - the result of blood disease, either spontaneous, or consequent upon infection by inflammatory products.

2. The fatty conversion of coagula development through similar agency, in the capillary system, as so-called depots - metastases.

3. In fibrinous and albuminous products of inflammation, - exudates, and especially pus. This is manifest in the exudates of serous membranes.

4. In the albuminous, fibrino-albuminous products of Bright's disease of the kidney. The spots involved in the process of fatty conversion are cognizable to the naked eye as dullish white, glistening, for the most part somewhat turgescent points.

5. In lardaceous infiltration of the liver. The lard-like blastema is seen here and there opaque, - of a dull white or whitish-yellow.

6. In tubercle, in incipient softening of the latter, and in like manner in crude fibrinous deposits.

7. In colloid, as met with frequently in the thyroid gland. In colloid of the more consistent kind, it is discernible with the naked eye as opaque, dull-white or whitish-yellow spots.

8. In cancers, where it enters into emulsion-like combinations with albumen, as also into saponaceous, glutinous conjunctions with bases - saponification of cancers. The points de depart are here the yellow, fibrinous masses which either traverse the cancer as a so-called reticulum, or else occur as circumscript accumulations.

9. In atheromatous disease, in the strata that form upon the inner surface of arteries, and in the soft matrix of phlebolites.

10. In the fibroid blastema and texture, more especially of fibroid tumors and exudates.

11. In the annulo-fibrous tunic of arteries, where it occurs, either pure or combined with, and dependent upon, stratiform deposits and their metamorphoses - atheroma and ossification.

12. In the muscles, especially the involuntary, and the heart in particular. Here we encounter an obvious conversion of the muscle-fibrils to molecular fat, with loss of the transverse striae and inflation of the sheaths.

Further investigations are necessary to determine whether milky blood - the peculiar aspect of which is due to fat; and whether the pellet-like excretion of fat from the intestine, should be classed along with the above.

This conversion into fat, affects, as we have seen, now crude fluid and solid blastemata, now such as have attained to various grades of tex-tural development; finally perfected textures.

The form or type under which the conversion takes place is very frequent, more especially in fluid blastemata. It has been described under the head of " metamorphoses of blastemata".

This process is in one sense to be regarded as a propitious event, as reducing certain growths to a condition readier for resorption and for re-assimilation. Moreover, it determines a state of involution, isolation, extinction of the involved growths.

In this latter property, it is often allied with ossification and cretefac-tion of blastemata and textures, - processes offering many points of analogy, and even of affinity with fatty disease from the disengagement of pre-existent fat. We need only advert to the cretefaction of crude blastemata in the coagula of the larger bloodvessels, and in the capillary system, in exudates, in pus, in tubercle, - to the ossification and cretefaction of stratiform deposits in the arteries, of the fibroid textures, etc, - and compare this process with the collateral one of fatty conversion.

Fats, the product of conversion, may present much variety of character. In most instances they are fluid fats in a state of minute molecular subdivision, in larger, lustrous, strongly refracting, - or else, in less bright, yellowish, tough globules. In exudates, in tubercle, in colloid substances, in cancers, and especially in the atheroma of arteries, cholesterine is frequently encountered in a crystalline state.