sule. The cells of this zone are polyhedral in shape, with granular protoplasm often containing fat droplets and with nuclei containing little chromatin. Similar cells are found in the reticular zone, but here they are found in small groups situated in the meshes of the reticulum. The cells of the medullary substance are less granular and smaller in size than those of the cortex, and are grouped in irregular, round, or oval masses bounded by the septa of reticulum. These cells stain a deep brown with chromic acid and its

Fig. 257.-Arrangement of the intrinsic blood-vessels in the cortex and medulla of the dog's adrenal (Fig. 17, Plate V, of Flint's article in "Contributions to the Science of Medicine," dedicated to Professor Welch, 1900).

salts, and the color can not be washed out with water-a peculiarity which shows itself even during the development of these elements, and which is possessed by few other types of cells. Numerous ganglion cells, isolated and in groups, and many nerve-fibers occur in this portion of the organ.

The blood-vessels of the suprarenal glands are of special interest, since it has been shown that the secretion of the glands passes directly or indirectly into the vessels. The following statements

we take from Flint: The blood-vessels, derived from various sources, form in the dog a poorly developed plexus, situated in the capsule. From this plexus three sets of vessels are derived, which are distributed respectively in the capsule, the cortex, and the medulla of the gland. The vessels of the capsule divide into capillaries, which empty into a venous plexus situated in the deeper portion of the capsule. The cortical arteries divide into capillaries which form networks, the meshes of which correspond to the arrangement of the cells in the different parts of the cortex, encircling the coiled columns of cells in the glomerular zone, while in the fascicular zone the capillaries are parallel with occasional anastomoses. These capillaries form a fine-meshed plexus in the reticular zone and unite in the peripheral portion of the medulla to form small anastomosing veins, from which the larger veins are derived. The latter do not anastomose, and are therefore terminal veins. The arteries of the medulla pass through the cortex without giving off any branches until the medulla is reached, where they break up into a capillary network surrounding the cell masses situated here. The blood from this plexus may be collected into veins of the medulla which empty into the terminal vein or some of its larger branches, or may flow directly into branches of the venous tree. The endothelial walls of the capillaries rest directly on the specific gland cells, with the intervention here and there of a few reticular fibrils. According to Pfaundler, the walls of the blood-vessels of the entire suprarenal body consist solely of the tunica intima.

The nerves of the suprarenal glands have been studied recently by Fusari and Dogiel (94); the description given by the latter will here be followed. Numerous nerve-fibers, both nonmedullated and medullated, arranged in the form of a plexus containing sympathetic ganglia, are found in the capsule. From this plexus numerous small bundles and varicose fibers enter the cortex, where they form plexuses surrounding the columns of cells or groups of cells found in the three zones of the cortex and about the vessels and capillaries of the cortex. The nerve-fibers of these plexuses are on the outside of the columns and cell groups and do not give off branches which pass between the cells. The nerve supply of the medullary substance is very rich, and is derived mainly from large nerve bundles which pass from the plexus in the capsule to the medulla, where they divide and form dense plexuses which surround the groups of gland-cells and veins; from these plexuses fine varicose fibers pass between the gland-cells, forming intercellular plexuses. In the medulla there are found in many animals large numbers of sympathetic cells, some isolated, others grouped to form small ganglia. Pericellular networks surround the cellbodies of certain of these sympathetic cells. (For further information concerning the suprarenal glands consult Gottschau, Weldon, Hans Rabl, C. K. Hoffmann (92), Pfaundler, Flint, and Dogiel.)

TECHNIC.

270. The arrangement of the cortical and medullary portions of the kidney is best seen in sections of the kidney of small mammalia, cut in the proper direction, and, if possible, embracing the whole organ. If, on the other hand, the finer epithelial structures are to be examined, small pieces are first fixed in osmic acid mixtures or in corrosive sublimate.

271. Impregnation with silver nitrate (method of Golgi or Cox) reveals some points as to the relation of the cells of the uriniferous tubules to each other.

272. In order to isolate the tubules, thin strips of kidney tissue are treated for from fifteen to twenty hours with pure hydrochloric acid having a specific gravity of 1.12 (for this purpose kidney tissue is used taken from an animal killed twenty-four hours previously). It is then washed, teased, and examined in glycerin (Schweiger-Seidel). Fuming nitric acid (40%), applied for a few hours to small pieces of tissue, occasionally isolates the uriniferous tubules very extensively. The further treatment is then the same as after hydrochloric acid. A 35% potassium hydrate solution may also be employed. The isolated pieces are, however, not easily preserved permanently.

273. The epithelium of the uriniferous tubules may be isolated either in alcohol (vid. T. 128) or, according to R. Heidenhain (83), in a 5% aqueous solution of neutral ammonium chromate. The latter method shows clearly the striation of the epithelium.

274. The autophysiologic injection with indigo-carmin (Chrzonszczewsky vid. T. 245), applied as in the case of the liver, fills the uriniferous tubules, which may then be further examined in sections.

275. The blood-vessels are examined in injected specimens (injection of the kidney is easily accomplished). In larger animals the injection is made into the renal artery, while in smaller ones the whole posterior half of the body is injected through the abdominal aorta.

276. The ureter and bladder are cut open, fixed, and then sectioned. In this way the organs are shown in a collapsed condition, in which the arrangement of the epithelium is totally different from that found in the distended organs. In order to observe them in the latter condition the fixing agent is injected into the ureter or bladder, when, after proper ligation, they are placed in the same fixing agent.

277. The usual fixing fluids are employed in the demonstration of the suprarenal capsule; but mixtures containing chromic acid, whether Flemming's fluid, chromic acid, or its salts, are of special importance in the examination of the organ, since the medullary substance of the suprarenal capsule stains a specific brown when treated by these mixtures (a condition only reduplicated in certain cells of the hypophysis). This brown staining also occurs when the cortical and medullary portions are entirely separated, as is the case in certain animals and during the development of the suprarenal capsule. The fat found in the cells of the suprarenal cortex is not identical with that of the rest of the body, as it may be dissolved by chloroform and oil of bergamot out of tissue fixed with osmic acid (Hans Rabl).

C. THE FEMALE GENITAL ORGANS.

1. THE OVUM.

The product of the ovaries is the matured "ovum," or egg, having a diameter of from 0.22 to 0.32 mm. It forms a single cell with a thick membrane, from 7 to 11μ in thickness, known as the zona pellucida. The ovum consists of a cell-body known as the yolk or vitellus, and a nucleus, from 30 μ to 40 μ in diameter, termed the germinal vesicle. The vitellus consists of two substances a protoplasmic network, with a somewhat denser arrangement at the periphery of the cell and in the neighborhood of the germinal vesicle, and of small, highly refractive, and mostly oval bodies imbedded between the meshes of the protoplasm-the yolk globules. These latter, as a rule, are merely browned on being treated with osmic acid, although occasionally a true fatty reaction may be obtained. The germinal vesicle is surrounded by a distinct membrane having a double contour. In its interior we find a scanty lining framework containing very little chromatin, and one or two relatively large false nucleoli, or germinal spots, from 7 to 10μ in diameter, due to a nodal thickening of the chromatin. In the latter a further very distinct differentiation is sometimes seen in the shape of a small body (vacuole ?) of doubtful origin, which has been called Schrön's granule. The germinal vesicle and spot were formerly known as "Purkinje's vesicle" and "Wagner's spot," respectively, from their discoverers.

2. THE OVARY.

The ovaries are almost entirely covered by peritoneum. The mesothelial cells of the latter, however, undergo here a differentiation, to form the germinal epithelium. At the hilum the peritoneal covering is absent, and it is here that the connective-tissue elements of the ovarian ligament penetrate into the organ to form its connective-tissue framework, the so-called stroma of the ovary. At an early period in the development of the ovaries, the germinal epithelium begins a process of invagination into the stroma of the ovary, so that at the periphery of the organ a zone is soon formed which consists of both connective tissue and epithelial (mesothelial) elements. This zone is called the cortex, or parenchymatous zone. That portion of the organ in the neighborhood of the hilum (aside from the rudimentary structure known as the epoophoron) consists of connective tissue containing numerous elastic fibers and unstriped muscle-cells, and is known as the medullary substance, or vascular zone. This connective tissue penetrates here and there into the cortex, separates the epithelial elements of the latter from each other, and is in direct continuation with a stratum immediately beneath the germinal epithelium, called the tunica albuginea. This latter layer of connective tissue is very distinct in the adult ovary, although its

In young

structure and thickness vary to a considerable extent. ovaries it is irregular, but shows in its highest development three layers distinguishable from each other by the different direction of the fibers. In the medullary substance the connective-tissue fibers are long, in the cortex short, and in the zone containing the follicles (see below) are mingled with numerous connective-tissue cells. Nonstriated muscle-fibers occur exclusively in the medulla. Here they are gathered in bundles which accompany the blood-vessels, and may even form sheaths around the latter. They are especially prominent in mammalia.

The germinal epithelium is distinguished from that of the remaining peritoneum by the greater height of its cells, which are

Fig. 258. Section from ovary of adult dog. At the right the stellate figure represents a collapsed follicle with its contents. Below and at the right are seen the tubules

of the parovarium (copied from Waldeyer).

cubic or even cylindric in shape. At an early period in the development of the ovaries this epithelium pushes into the underlying embryonic connective tissue in solid projections, to form the primary egg tubes of Pflüger, the cells of which very soon begin to show differentiation. Some retain their original characteristics and shape, while others increase in size, become rounded, and develop into the young ova. Those retaining their indifferent type become the follicular cells surrounding the egg. This differentiation into ova and follicular elements may even occur in the germinal epithelium itself, in which case the larger round cells are known as the primitive or primordial ova. In the further development of the ovarian cortex