(3) Granular Casts.--These are merely hyaline casts in which numerous granules are embedded (Figs. 42, 44, 46, and 61). _Finely granular casts_ contain many fine granules, are usually shorter, broader, and more opaque than the hyaline variety, and are more conspicuous. Their color is grayish or pale yellow. [Illustration: FIG. 44.--Granular and fatty casts and two compound granular cells (Stengel).] _Coarsely granular casts_ contain larger granules and are darker in color than the finely granular, being often dark brown owing to presence of altered blood-pigment. They are usually shorter and more irregular in outline, and more frequently have irregularly broken ends. (4) Fatty Casts.--Small droplets of fat may at times be seen in any variety of cast. Those in which the droplets are numerous are called fatty casts (Figs. 43 and 44). The fat-globules are not difficult to recognize. Staining with osmic acid or Sudan (p. 109) will remove any doubt as to their nature. {118} The granules and fat-droplets seen in casts are products of epithelial degeneration. Granular and fatty casts, therefore, always indicate partial or complete disintegration of the renal epithelium. The finely granular variety is the least significant, and is found when the epithelium is only moderately affected. Coarsely granular, and especially fatty casts, indicate a serious parenchymatous nephritis. (5) Casts Containing Organized Structures.--Cells and other structures are frequently seen adherent to a cast or embedded within it. (See Figs. 41 and 42). When numerous, they give name to the cast. (_a_) _Epithelial casts_ contain epithelial cells from the renal tubules. They always imply desquamation of epithelium, which rarely occurs except in parenchymatous inflammations (Figs. 60 and 61). [Illustration: FIG. 45.--Red blood-corpuscles and blood-casts (courtesy of Dr. A. Scott) (obj. one-sixth) (Boston).] (_b_) _Blood-casts_ contain red blood-corpuscles, usually much degenerated (Figs. 45 and 60). They always indicate hemorrhage into the tubules, which is most {119} common in acute nephritis or an acute exacerbation of a chronic nephritis. (_c_) _Pus-casts_ (see Fig. 62), composed almost wholly of pus-corpuscles, are uncommon, and point to a chronic suppurative process in the kidney. (_d_) True _bacterial casts_ are rare. They indicate a septic condition in the kidney. Bacteria may permeate a cast after the urine is voided. [Illustration: FIG. 46.--Hyaline and granular casts, mucous threads, and cylindroids. There are also a few epithelial cells from the bladder (Wood).] The structures most likely to be mistaken for casts are: