If my readers will turn to the chapter in which the structure of the kidney is described, it will be found that that organ is represented as performing the part of a scavenger and a filter in the body. It will be remembered that the arterial blood is brought by the short arteries of the kidney straight from the main current into a close tangle of loops of blood vessels called a glomerulus. This glomerulus is pushed into the blind and expanded head of a long uriniferous tubule. The cells lining this bag-like end of the tubule are small and flat, and they act merely as a filter. The blood, carried with considerable force straight from the renal artery, is brought to a sudden condition of stasis in the loops of the glomerulus, and it can be easily understood how that, under these circumstances, the blood parts with a good deal of its fluid. What, however, passes from the blood is not its nutritive constituent parts, but its excess of water and the excretory products with which it is laden. These products are specially urea and urates, which are, as has been already fully explained, the final products of the digestion of albuminous foods.

Now, if instead of the blood parting only with urea and water in the kidney, it allowed the albumen, which forms its most important nutritive constituent, to pass across the filter into the uriniferous tubules, and if at the same time the excretory products of urea and urates were retained in the blood, an abnormal condition, highly prejudicial to health, would be present; for there would be an extravagant waste of albumen, out of which the blood reconstructs the tissues and fluids of the body, and the blood instead of being cleansed in the kidney would remain charged with the poisonous products of combustion. This is what occurs in chronic Bright's disease. The kidney is damaged; it fails to separate the urea from the blood, and it allows the albumen to escape into the tubules.