URINARY ANALYSIS. INTRODUCTION. The urine is an aqueous solution of organic and inorganic substances excreted and secreted by glands called the kidneys. Assuming that the reader is acquainted with the gross and minute structure of the kidneys, it remains for us to consider some of the physiologic processes which are concerned in the production of the urine. The very close relation which exists between the blood-vessels and the uriniferous tubules suggests at once the fact that the fluid called urine is the product of nature's effort to remove from the body, by way of the blood, those substances which are no longer useful to the tissues of the body; in other words, the urine is essentially a solution of wasteproducts of the body. Having carefully studied the minute structure of the kidneys, we find that, unlike other secreting organs, they consist of two parts, so distinct in structure that it seems almost impossible to resist the conclusion that their functions are different, and that the mechanism by which the urine is secreted is of a double kind. The uriniferous tubules, on the one hand, with their characteristic epithelium, appear to be merely secreting structures; while, on the other hand, the Malpighian capsules with their glomeruli are structures with insignificant epithelium, strongly suggesting that their function is rather one of the nature of a filter than of a secreting structure. Such is the theory of Bowman, since he first pointed out that certain constituents of the urine only are put forth by the uriniferous tubules, which act in a manner similar to other secreting glands, and that the other constituents, including water and various soluble and diffusible salts from the blood, are apparently filtered out by the glomeruli. It is very evident from the vascular arrangement in the kidney that the capacity of the kidney for work is closely dependent on the flow of blood through it, and this appears to be controlled largely by the vasomotor and vasodilator nerves, which are supplied by the anterior roots of the eleventh, twelfth, and thirteenth dorsal nerves. The theory of Ludwig, based on the varying degrees of blood pressure in the glomeruli, and the elimination of certain constituents of the blood by diffusion or osmosis, can hardly be considered tenable in the light of recent physiologic research. In this theory Ludwig did not consider the importance of the renal epithelium in the secretion of urine, as has been well demonstrated by the experiments of Heidenhain, who found that by injecting a solution of sodium indigo-sulphate into the blood of an animal not only the urine became blue, but the epithelial cells lining the convoluted tubules and the looped tubes of Henle were also colored blue, while there was not the slightest trace of blue in the Malpighian bodies. By first dividing the spinal cord of an animal and then injecting the indigo solution, he also demonstrated the fact that the renal epithelium has distinct eliminative power. He found the following: That no urine reached the bladder, and the epithelium lining the convoluted tubules as well as those of Henle was stained blue the same as before; that when the animal was killed, a sufficient period after the injection, the epithelium was found to be free from coloring-matter, and the indigo compound had passed into the lumen of the tubules, where, in the absence of water from the glomeruli, it had crystallized. It often happens in some diseases of the kidneys in which the renal tubules become stripped of their epithelium that the urea and other products of the metabolism are no longer so thoroughly removed from the body, but remain in the blood, and frequently cause the symptom known as uremia, often when the watery constituent is eliminated in abundance. It is, therefore, fair to conclude that the renal epithelial cells are normally actively engaged in the process of secretion, and that the water and some of the soluble salts of the urine are secreted largely by the glomeruli, the function of which is regulated chiefly by the varying degrees of blood pressure. Too much can not be said regarding the importance of an accurate examination of the urine,-both chemic and |