These substances crystallize in very slender needles, which are sometimes straight, but more often somewhat curved or wavy in their outline. (Fig. 7.)

They are always deposited in a more or less radiated form; and have sometimes a very elegant, branched, or arborescent arrange

ment.

When in a fluid state, the fatty substances present themselves

Fig. 8.

O

O

OLEAGINOUS PRINCIPLES OF HUMAN FAT. Stearine and

Margarine crystallized; Oleine Fluid.

under the form of drops or
globules, which vary indefi-
nitely in size, but which
may be readily recognized
by their optical properties.
They are circular in shape,
and have a faint amber color,
distinct in the larger globules,
less so in the smaller. They
have a sharp, well defined
outline (Fig. 8); and as they
refract the light strongly,
and act therefore as double
convex lenses, they present
a brilliant centre, surrounded
These
by a dark border.
marks will generally be

sufficient to distinguish them under the microscope.

The following list shows the percentage of oily matter present in

various kinds of animal and vegetable food.1

QUANTITY OF FAT IN 100 PARTS IN

The oleaginous matters present a striking peculiarity as to the form under which they exist in the animal body; a peculiarity which distinguishes them from all the other proximate principles. The rest of the proximate principles are all intimately associated together by molecular union, so as to form either clear solutions or

Pereira, op. cit., p. 81.

homogeneous solids. Thus, the sugars of the blood are in solution in water, in company with the albumen, the phosphate of lime, chloride of sodium, and the like; all of them equally distributed throughout the entire mass of the fluid. In the bones and cartilages, the animal matters and the calcareous salts are in similarly intimate union with each other; and in every other part of the body the animal and inorganic ingredients are united in the same way. But it is different with the fats. For, while the three principal varieties of oleaginous matter are always united with each other, they are not united with any of the other kinds of proximate principles; that is, with water, saline substances, sugars, or albuminous matters. Almost the only exception to this is in the nervous tissue; in which, according to Robin and Verdeil, the oily matters seem to be united with an albuminoid substance. Another exception is, perhaps, in the bile; since some of the biliary salts have the power of dissolving a certain quantity of fat. Everywhere else, instead of forming a homogeneous solid or fluid with the other proximate principles, the oleaginous matters are found in distinct masses or globules, which are suspended in serous fluids, interposed in the interstices between the anatomical elements, included in the interior of cells, or deposited in the substance of fibres or membranes. Even in the vegetable tissues, the oil is always deposited in this manner in distinct drops or granules.

Owing to this fact, the oils can be easily extracted from the organized tissues by the employment of simply mechanical processes. The tissues, animal or vegetable, are merely cut into small pieces and subjected to pressure, by which the oil is forced out from the parts in which it was entangled, and separated, without any further manipulation, in a state of purity. A moderately elevated temperature facilitates the operation by increasing the fluidity of the oleaginous matter; but no other chemical agency is required for its separation. Under the microscope, also, the oil drops and granules can be readily perceived and distinguished from the remaining parts of the tissue, and can, moreover, be easily recognized by the dissolving action of ether, which acts upon them, as a general rule, without attacking the other proximate principles.

Oils are found, in the animal body, most abundantly in the adipose tissue. Here they are contained in the interior of the adipose vesicles, the cavities of which they entirely fill, in a state

Fig. 9.

to

of health. These vesicles are transparent, and have a somewhat angular form, owing to their mutual compression. (Fig. 9.) They vary in diameter, in the human subject, from of an inch, and are composed of a thin, structureless animal membrane, forming a closed sac, in the interior of which the oily matter is contained. There is here, accordingly, no union whatever of the oil with the other proximate principles, but only a mechanical inclusion of them by the walls of the vesicles. Sometimes, when emaciation is going on, the oil partially disappears from

HUMAN ADIPOSE TISSUE.

the cavity of the adipose vesicle, and its place is taken by a watery serum; but the serous and oily fluids always remain distinct, and occupy different parts of the cavity of the vesicle.

In the chyle, the oleaginous matter is in a state of emulsion or suspension in the form of minute particles in a serous fluid. Its

Fig. 10.

CHYLE, from commencement of Thoracic Duct, from

the Dog.

subdivision is here more complete, and its molecules more minute than anywhere else in the body. It presents the appearance of a fine granular dust, which has been known by the name of the "molecular base of the chyle." A few of these granules are to be seen which measure roboo of an inch in diameter; but they are generally much less than this, and the greater part are so small that they cannot be accurately measured. (Fig. 10.) For the same reason they do not present the bril

liant centre and dark border of the larger oil-globules; but appear

by transmitted light only as minute dark granules. The white color and opacity of the chyle, as of all other fatty emulsions, depend upon this molecular condition of the oily ingredients. The albumen, salts, &c., which are in intimate union with each other, and in solution in the water, would alone make a colorless and transparent fluid; but the oily matters, suspended in distinct par ticles, which have a different refractive power from the serous fluid, interfere with its transparency

and give it the white color and opaque appearance which are characteristic of emulsions. The oleaginous nature of these particles is readily shown by their solubility in ether.

In the milk, the oily matter occurs in larger masses than in the chyle. In cow's milk (Fig. 11), these oil-drops, or "milk-globules," are not quite fluid, but have a pasty consistency, owing to the large quantity of margarine which they contain, in proportion to

Fig. 11.

GLOBULES OF Cow's MILK.

the oleine. When forcibly amalgamated with each other and

collected into a mass by prolonged beating or churning, they con

stitute butter. In cow's milk,

the globules vary somewhat in size, but their average diameter is ooo of an inch. They are simply suspended in the serous fluid of the milk, and are not covered with any albuminous membrane.

In the cells of the laryngeal, tracheal, and costal cartilages (Fig. 12), there is always more or less fat deposited in the form of round-duide ed globules, somewhat similar to the milk. th

Fig. 12.

CELLS OF COSTAL CARTILAGES, containing Oil-Globules.

In the glandular cells of the liver, oil occurs constantly, in a state of health. It is here deposited in the substance of the cell

Fig. 13.

HEPATIC CELLS. Human.

(Fig. 13), generally in smaller
globules than the preceding.
In some cases of disease, it
accumulates in
in excessive
quantity, and produces the
state known as fatty degene-
ration of the liver. This is
consequently only an ex-
aggerated condition of that
which normally exists in
health.

In the carnivorous animals, oil exists in considerable quantity in the convoluted portion of the uriniferous tubules. (Fig. 14.) It

is here in the form of granules and rounded drops, which sometimes appear to fill nearly the whole calibre of the tubules.

It is found also in the secreting cells of the sebaceous and other

cause of the peculiar color of this body.

It occurs also in the form of granules and oil-drops in the muscular fibres of the uterus (Fig. 15), in which it begins to be