It has been pointed out that tube casts are usually present in Bright's disease, whatever the form or stage, and they are known to afford important indications in the urine passed by patients affected by this disease. But they exist in other conditions besides Bright's disease. They are not infrequently present in passive hyperemia of the kidney, and are seen also in simple atrophic conditions.

They form cylindrical casts of the tubules, composed of a clear translucent hyaline material, which, however, may contain in its substance, epithelium, fat, blood, and other matters which are present in the tubules, so that we may have hyaline, epithelial, granular, fatty, or blood casts, all of which may be found in the urine.

The tube casts are for the most part due to exudation from the glomeruli. They usually coincide with the occurrence of albumen in the urine, and they probably arise chiefly by coagulation of the serum-albumen which has transuded into the tubules. They are sometimes called fibrine cylinders, and their discoverer, Henle, regarded them as composed of fibrine. But they do not conform to the characters of fibrine, and as they occur in cases in which there is little or no inflammation they can hardly represent a fibrinous exudation.

Besides this origin they may be derived from the epithelium of the tubules, either by a kind of secretion from the epithelium or by a colloid transformation.

The tube casts which pass into the urine come chiefly from the straight tubules, including the loops of Henle. Those from the convoluted tubules, being thicker and having to pass the narrow loop, are less likely to be carried outwards, although being soft and plastic they may accommodate themselves and so pass outwards.