Some observers believe that albumen is always present in the urine, but in such small amounts as to elude the ordinary tests. Both physiological and pathological albuminuria is most constant and abundant after eating. The albumen is not all of the same character. Most of it is serum-albumen, but with it is a smaller amount of globulin and sometimes of peptones. As yet the serum-albumen seems to be of the principal practical importance. Pathological albuminuria is most constant and the albumen is most abundant with acute and chronic parenchymatous nephritis, with acute diffuse nephritis, and with the large white variety of chronic diffuse nephritis. It is least constant and least abundant with the atrophic variety of chronic diffuse nephritis, with some waxy kidneys, with interstitial nephritis, and with chronic congestion of the kidney. A variety of explanations have been given to account for the production of albumen by diseased kidneys, but none of them are very satisfactory. The albuminuria has been ascribed to disease of the epithelium of the Malpighian bodies; to increase of the blood-pressure within the renal arteries, either with or without disease of the arterial walls; to slowing of the blood-current in the arteries; to diminution of the blood-pressure in the arteries; to congestion of the renal veins; to changes in the {76} composition of the blood; to changes in the epithelium of the renal tubules. For practical purposes it is to be remembered that large amounts of albumen regularly indicate structural changes in the kidneys; that small amounts of albumen are found without any kidney lesions, with chronic congestion of the kidney, and with chronic diffuse nephritis; that chronic diffuse nephritis may exist without albuminuria for a long time. In many cases of kidney disease we find in the urine bodies of cylindrical shape called casts. The same bodies are also found within the tubules of diseased kidneys. Concerning the nature and origin of these bodies we are still ignorant. We only know that they are formed within the kidney tubules and are carried thence into the urine. With the exception of the blood-casts, which are composed simply of a number of blood-globules pressed together, all casts seem to be formed of a peculiar homogeneous hyaline substance to which other elements may be added. Hyaline casts are composed entirely of such material. Waxy casts are formed of the same substance, which becomes denser. Epithelial casts are made by the adhesion of epithelial cells to the surface of hyaline casts. Nucleated, granular, and fatty casts are hyaline casts with the fragments of degenerated epithelium incorporated in them.