nal products of the disassimilation of albuminous compounds, and is probably produced in the liver.

Hippuric acid is found very generally in urine, though it is present only in small amounts. It is increased by a diet of asparagus, cranberries plums, and by the administration of benzoic and cinnamic acids. It is probably formed in the kidney.

Kreatinin resembles the kreatin derived from muscles. It is a colorless crystal, belonging to the rhombic system. Its origin is unknown, though it is largely increased in amount by albuminous food. About 15 grains are excreted daily.

Xanthin, Sarkin, Oxaluric Acid, and Allantoin are also constituents of urine. They are nitrogenized compounds and are also terminal products of albuminous compounds.

Urobilin, the coloring matter of the urine, is a derivative of the bile pigIt is particularly abundant in febrile conditions, giving to the urine

ments.

its reddish-yellow color.

Inorganic Constituents of Urine.-Earthy Phosphate. Phosphoric acid in combination with magnesium and calcium is excreted daily to the extent of from 15 to 30 grains. The phosphates are insoluble in water, but are held in solution in the urine by its acid ingredients, alkalinity of the urine being attended with a copious precipitation of the phosphates. Mental work increases the amount of phosphoric acid excreted, a condition caused by increased metabolism of the nervous tissue.

Sulphuric acid in combination with sodium and potassium constitute the sulphates, of which about 30 grains are excreted daily. Sulphuric acid results largely from the decomposition of albuminous food and from increased destruction of animal tissues.

The Gases of the urine are carbonic acid and nitrogen.

Mechanism of Urinary Secretion.-As the kidney anatomically presents an apparatus for filtration (the Malpighian bodies), and an apparatus for secretion (the epithelial cells of the urinary tubules), it might be inferred that the elimination of the constituents of the urine is accomplished by the twofold process of filtration and secretion; that the water and highly diffusible inorganic salts simply pass by diffusion through the walls of the blood-vessels of the glomerulus into the capsule of Müller, while the urea and remaining organic constituents are removed by true secretory action of the renal epithelium. Modern experimentation supports this view of renal action.

T

The secretion of urine is therefore partly physical and partly vital.

The filtration of urinary constituents from the glomerulus into Müller's capsule depends largely upon the blood pressure and the rapidity of blood flow in the renal artery and glomerulus. Among the influences which increase the pressure and velocity, may be mentioned increased frequency and force of the heart's action, contraction of the capillary vessels of the body generally, dilatation of the renal artery, increase in the volume of the blood.

The reverse conditions lower the blood pressure and diminish the secretion of urine.

The elimination of the organic matters by secretory activity of the renal epithelium seems to be well established by modern experiments. These substances, removed from the blood in the secondary capillary plexus of blood-vessels, by a true selective action of the epithelium, are dissolved and washed toward the pelves by the liquid coming from the capsules.

The blood supply to the kidney is regulated by the nervous system. If the renal nerves be divided, the renal artery dilates and a copious flow of urine takes place. If the peripheral ends of the same nerves be stimulated the artery contracts and the urinary flow ceases. The same is true of the splanchnic nerves, through which the vasomotor nerves coming from the medulla oblongata and spinal cord pass to the renal plexus.

LIVER.

The Liver is a highly vascular, conglomerate gland, appended to the alimentary canal. It is the largest gland in the body, weighing about 41⁄2 pounds; it is situated in the right hypochondriac region, and retained in position by five ligaments, four of which are formed by duplicatures of the peritoneal investment.

The proper coat of the liver is a thin but firm fibrous membrane, closely adherent to the surface of the organ, which it penetrates at the transverse fissure, and follows the vessels in their ramifications through its substance, constituting Glisson's capsule.

Structure of the Liver.-The liver is made up of a large number of small bodies, the lobules, rounded or ovoid in shape, measuring the of an inch in diameter, separated by a space in which are situated bloodvessels, nerves, hepatic ducts, and lymphatics.

The Lobules are composed of cells, which, when examined microscopically, exhibit a rounded or polygonal shape, and measure, on the average, the of an inch in diameter; they possess one, and at times two, nuclei;