The nervous system controls the enlargement of the spleen; division of the nerve produces dilatation of the vessels, stimulation contracts them.

The Supra-renal Capsules are triangular, flattened bodies, situated above the kidney. They are invested by a fibrous capsule sending in trabeculæ, forming the framework. The glandular tissue is composed of two portions, a cortical and medullary. The cortical being made up of small cylinders lined by cells and containing an opaque mass, nuclei and granular matter. The medullary consists of a fibrous network containing in the alveoli nucleated protoplasm.

The Thyroid gland consists of a fibrous stroma, containing ovoid closed sacs, measuring on the average of an inch, formed of a delicate membrane lined by cells; the contents of the sacs consist of yellowish albuminous fluid.

The Thymus gland is most developed in early life and almost disappears in the adult. It is divided by processes of fibrous tissue into lobules, and these again into follicles which contain lymphoid corpuscles.

The functions of the vascular glands appear to be the more complete elaboration of the blood necessary for proper nutrition; they are most highly developed during infancy and embryonic life, when growth and development are most active.

EXCRETION.

The Principal Excrementitious Fluids discharged from the body are the urine, perspiration and bile; they hold in solution principles of waste which are generated during the activity of the nutritive process, and are the ultimate forms to which the organic constituents are reduced in the body. They also contain inorganic salts.

The Urinary Apparatus consists of the kidneys, ureters and bladder.

KIDNEYS.

The Kidneys are the organs for the excretion of urine; they resemble a bean in shape, are from four to five inches in length, two in breadth, and weigh from four to six ounces.

They are situated in the lumbar region, one on each side of the vertebral column, behind the peritoneum, and extend from the 11th rib to the crest of the ilium; the anterior surface is convex, the posterior concave, and presents a deep notch, the hilum.

The kidney is surrounded by a thick layer of fat, beneath which is the

fibrous coat, thin and smooth, composed of dense white fibrous tissue with which are intermingled elastic fibres. It is adherent to the surface of the organ, but can easily be removed by dissection.

Longitudinal section through the kidney, the pelvis of the kidney, and a number of renal calyces. A, branch of the renal artery; U, ureter; C, renal calix; 1, cortex; 1', medullary rays; 1", labyrinth, or cortex proper; 2, medulla; 2', papillary portion of medulla, or medulla proper; 2", border layer of the medulla; 3, 3, transverse section through the axes of the tubules of the border layer; 4, fat of the renal sinus; 5, 5, arterial branches; *, transversely coursing medulla rays.-Tyson, after Henle.

The Substance of the Kidney is dense, but friable; upon making a longitudinal section, and dividing it, there is presented a cavity, the

pelvis, lined by the proper fibrous coat and occupied by the expanded portion of the ureter.

The kidney exhibits two structures, viz. :—

1. An external or cortical portion, about 6 of an inch in diameter, of a reddish color, and somewhat granular.

2. An internal or medullary portion, of a dark red color, arranged in the form of pyramids, the bases of which are directed toward the cortical portion, and the apices toward the pelvis, into which they project, and are covered by the calyces.

The Cortical portion of the kidney consists of a delicate matrix containing an immense number of tubules, having a markedly convoluted appearance, and interlacing in every direction (the tubules of Ferrein). Throughout its structure are numerous ovoid bodies, the Malpighian bodies, which are the flask-like terminations of the convoluted tubules;

FIG. 9.

Diagrammatic exposition of the method in which the uriniferous tubes unite to form primitive cones.-Tyson, after Ludwig.

these tubes are composed of a delicate homogeneous membrane lined by nucleated cells. After pursuing a most intricate course in the cortical portion, they become narrower and form loops which dip into the pyramidal portion (Henle's tubules), returning upon themselves, to finally terminate in the straight tubes of the pyramids.

The Malpighian bodies, the dilated extremities of the convoluted tubes, consist of a little sac (the capsule of Müller), which is ovoid in shape, measuring about the of an inch in diameter, and contains a tufted mass of minute blood vessels, over the surface of which is reflected a layer of cells.

Medullary Substance. The conical masses, the pyramids of Malpighi, consist of a number of straight tubes, which commence at the apex by from 10 to 20 openings; and as they pass toward the cortical portion, they divide and subdivide at acute angles, until a large mass of tubes is

produced. These tubes are on the average about of an inch in diameter, and composed of a thin, but firm, elastic, structureless membrane, lined by polygonal nucleated cells, which reduce the diameter of the lumen of the tube about two-thirds; these are the straight tubes of Bellini.

Blood vessels of the Kidney. The renal artery is of large size and enters the organ at the hilum; it divides into several large branches, which penetrate the substance of the kidney, between the pyramids, at the base of which they form an anastomosing plexus, which completely surrounds them. From this plexus vessels follow the straight tubes toward the apex, while others entering the cortical portion, divide into small twigs which enter the Malpighian body and form a mass of convoluted vessels, the glomerulus. After circulating through the Malpighian tuft the blood is gathered together by two or three small veins, which again subdivide and form a fine capillary plexus, which envelops the convoluted tubules; from this plexus the veins converge to form the emulgent vein, which empties into the vena cava.

The nerves of the kidney follow the course of the blood vessels and are derived from the renal plexus.

The Ureter is a membranous tube, situated behind the peritoneum, about the diameter of a goose quill, 18 inches in length, and extends from the pelvis of the kidney to the base of the bladder, which it perforates in an oblique direction. It is composed of 3 coats, fibrous, muscular and

mucous.

The Bladder is a temporary reservoir for the reception of the urine prior to its expulsion from the body; when fully distended it is ovoid in shape, and holds about one pint. It is composed of four coats, serous, muscular, the fibres of which are arranged longitudinally and circularly, areolar and mucous. The orifice of the bladder is controlled by the sphincter vesica, a muscular band, about half an inch in width.

As soon as the urine is formed it passes through the tubuli uriniferi into the pelvis, and from thence through the ureters into the bladder, which it enters at an irregular rate. Shortly after a meal, after the ingestion of large quantities of fluid, and after exercise, the urine flows into the bladder quite rapidly, while it is reduced to a few drops during the intervals of digestion. It is prevented from regurgitating into the ureters on account of the oblique direction they take between the mucous and muscular

coats.

Nervous Mechanism of Urination. When the urine has passed into the bladder it is there retained by the sphincter vesica muscle kept in a state of tonic contraction by the action of a nerve centre in the lumbar region of the spinal cord. This centre can be inhibited and the sphincter relaxed, either reflexly, by impressions coming through sensory nerves from the mucous membrane of the bladder, or directly, by a voluntary impulse descending the spinal cord. When the desire to urinate is experienced, impressions made upon the vesical sensory nerves are carried to the centres governing the sphincter and detrusor urinæ muscles and to the brain. If now the act of urination is to take place, a voluntary impulse, originating in the brain, passes down the spinal cord and still further inhibits the sphincter vesicæ centre, with the effect of relaxing the muscle, and of stimulating the centre governing the detrusor muscle, with the effect of contracting the muscle and expelling the urine. If the act is to be suppressed voluntary impulses inhibit the detrusor centre and possibly stimulate the sphincter centre.

The genito-spinal centre controlling these movements is situated in that portion of the spinal cord corresponding to the origin of the 3d, 4th and 5th sacral nerves.

URINE.

Normal Urine is of a pale yellow or amber color, perfectly transparent, with an aromatic odor, an acid reaction, a specific gravity of 1.020, and a temperature when first discharged of 100° Fahr.

The color varies considerably in health, from a pale yellow to a brown hue, due to the presence of the coloring matter, urobilin or urochrome. The transparency is diminished by the presence of mucus, the calcium and magnesium phosphates and the mixed urates.

The reaction is slightly acid, caused by the acid phosphate of sodium. After standing for a short time, an increased acidity is observed, due to an acid fermentation, from the presence of mucus. The urea is converted into ammonium carbonate, giving rise to a strong ammoniacal odor.

The specific gravity varies from 1.010 to 1.025.

The quantity of urine excreted in 24 hours is between 40 and 50 fluid ounces, but ranges above and below this standard.

The odor is characteristic, and caused by the presence of taurylic and phenylic acids, but is influenced by vegetable foods and other substances eliminated by the kidneys.