PATHOLOGIC HISTOLOGY.

I. THE ORGANS OF CIRCULATION.

HEART.

The heart-wall consists of three layers: the epicardium, myocardium, and endocardium. The epicardium (visceral portion of the pericardium) is composed of connective-tissue fibers, and is covered on its outer surface by flat, irregular, polygonal epithelium. [Throughout this book the word epithelium is used in the morphologic sense. Underneath the epicardium lies, normally, at various places a distinct layer of fat-cells. The elastic fibers of the auricular epicardium are lost in the adventitia of the larger venous trunks.

The myocardium is made up of short, cylindric, transversely striated muscle-cells. As in the voluntary muscles, they consist of isotropic and anisotropic transverse bands, which alternate. The protoplasm is divided into a peripheral, longitudinally striated, fibrillar substance and a central portion-the sarcoplasm. In the latter lies the oval, vesicular nucleus, around which is usually seen a small deposit of fine, granular, brownish pigment. A cell-membrane-the so-called sarcolemma-is absent in the heart-muscle of man. Many muscle-cells are united with one another through oblique and transverse branches.

The endocardium is composed, like the epicardium, of

an avascular connective-tissue membrane, containing, especially in the auricles, a great number of elastic elements with a few smooth muscle-fibers. It is lined on its inner surface by a layer of polygonal, flattened epithelium. The heart-valves are reduplications of the endocardium with strongly developed elastic fibers. Blood-vessels are not found normally in the valves of the full grown; in the case of the auriculoventricular valves, blood-vessels reach to the bases.

In the fetus, however, as well as in the new-born, the leaflets are richly supplied with blood-vessels up to their free borders. Along the lines of closure the connective tissue is soft and myxomatous, and is composed of numerous stellate cells which anastomose with one another. Here are formed the fetal, gelatinous nodules which sometimes are mistaken for endocardial inflammatory processes. Later, the blood-vessels disappear, and the gelatinous nodules are transformed into fibrous nodules, which are never missed at the borders of the tricuspid and mitral leaflets. (Plate 5, Fig. I.)

Diseases of the Heart-muscle.

In the course of the acute general infectious diseases (sepsis, typhoid, diphtheria, scarlatina, variola, etc.) there occurs quite frequently in the myocardium an albuminous degeneration, or so-called cloudy swelling, as is the case in the large parenchymatous organs. Microscopically, the fresh preparations show enlargement of the individual muscle-cells. The cement lines appear more distinctly and are broader than normal, while the nuclei and the transverse striæ are indistinct or entirely obscured. The protoplasm contains an enormous number of very fine granules, of a dust-like, opaque, grayish appearance. the addition of weak solution of acetic acid this cloudiness immediately clears up, owing to the transformation

On

of the albuminous granules into acid albumin, which becomes dissolved in the residual acid. The striations and nuclei now become distinctly visible. In stained preparations this cloudy swelling is not seen.

Cloudy swelling is frequently a forerunner, or intermediate stage, of a more deep-seated degenerative process of the heart-muscle-namely, fatty degeneration. This may occur independently of cloudy swelling. It may be either circumscribed or diffuse. Usually, it is found in patches in the form of wavy lines, parallel with the longitudinal axis of the muscle-bundles, giving the muscle an appearance similar to that of a tiger's skin, the degenerated areas appearing light in color. Fatty degeneration may result from local disturbance of nutrition, such as may follow narrowing or occlusion of the coronary vessels, or from the pressure of pericardial exudate. It may occur from acute intoxications: the most important toxic agents in this respect are phosphorus and arsenic ; less frequently, chloroform, ether, and alcohol; and it is found quite frequently also in the course of the acute infectious diseases, through the action of bacterial toxins; furthermore, in all diseases that lead to a diminution or destruction of the blood, such as pernicious anemia and the severer forms of leukemia. Microscopic examination of fresh preparations will show that the muscle-cells are filled with fine, round, highly refractile globules, which are arranged parallel with the longitudinal fibrils, and which may completely cover the nuclei as well as the transverse striæ. On the addition of acetic acid or potassium hydrate the granules do not become dissolved, showing that they are fat-globules. In long-standing and severe cases the individual droplets run together, forming large drops. The fat-globules are easily pressed out of the cells, after which are seen only their shadows or outlines in the cell. In the latter the transverse striæ are completely lost; the longitudinal striations, however, may still be present.

PLATE 1.

FIG. I.-Fatty Degeneration of the Heart-muscle in Acute Pernicious Anemia. Fresh teased preparation. X 340. In the center are seen muscle-fibers totally filled with fat-globules; the fibers are partly ruptured. Transverse striations are not discernible. Above and to the left a fiber is seen, out of which the fat-globules are partly extruded; here the longitudinal striation is still noticed. Free, large fat drops are seen; below and to the right, several slightly degenerated fibers still containing transverse striæ.

FIG. II. From the Same Case. Frozen sections of a papillary muscle of the mitral valve. Stained with sudan III. 340. The fat-droplets are stained orange-red. Here and there are seen the degenerated areas; above and to the right, almost normal musclefibers.

In frozen preparations stained with sudan III the degenerated areas are well differentiated from the normal striated muscle-fibers.

Fatty degeneration must not be confounded with increase of fat in the normal subepicardial fat-layer-adipositas cordis or obesitas, also known as lipomatosis cordis ; here the fat does not appear in globules, but as distinct fat-cells and as an independent tissue. It infiltrates the heart-wall in clusters, extending toward the endocardium. In severe cases it appears especially over the right ventricle and below the endocardium. The musculature becomes compressed, pushed aside, is frequently atrophied, and substituted by fat. The muscle-fibers may decrease to one-half or two-thirds their normal size; the striations, however, being well preserved. At times, especially in corpulent individuals, it is very hard to distinguish between physiologic and pathologic infiltration or deposition of fat. Usually, the finding of atrophied muscle-bundles between rows of fat-cells will differentiate these conditions.

A quite common, almost physiologic, condition, found in advanced age, is brown atrophy of the heart-muscle.