* * * * * 2. Bile.--Normally, unaltered bile-pigment is never present in the feces of adults. In catarrhal conditions of the small intestine bilirubin may be carried through unchanged. It may be demonstrated by filtering (after mixing with water if the stool be solid) and testing the filtrate by Gmelin's method, as described under The Urine. III. MICROSCOPIC EXAMINATION Care must be exercised in selection of portions for examination. A random search will often reveal nothing of interest. A small bit of the stool, or any suspicious-looking particle, is placed upon a slide, softened with water if necessary, and pressed out into a thin layer with a cover-glass. A large slide--about 2 by 3 inches--with a correspondingly large cover will be found convenient. Most of the structures which it is desired to see can be found with a two-thirds objective. Details of structure must be studied with a higher power. {240} The bulk of the stool consists of granular débris. Among the recognizable structures met in normal and pathologic conditions are: remnants of food, epithelial cells, pus-corpuscles, red blood-corpuscles, crystals, bacteria, and ova of animal parasites (Fig. 90). [Illustration: FIG. 90.--Microscopic elements of normal feces: _a_, Muscle-fibers; _b_, connective tissue; _c_, epithelial cells; _d_, white blood-corpuscles; _e_, spiral vessels of plants; _f_-_h_, vegetable cells; _i_, plant hairs; _k_, triple phosphate crystals; _l_, stone cells. Scattered among these elements are micro-organisms and débris (after v. Jaksch).] 1. Remnants of Food.--These include a great variety of structures which are very confusing to the student. Considerable study of normal feces is necessary for their recognition. _Vegetable fibers_ are generally recognized from their spiral structure; _vegetable cells_, from their double contour and the chlorophyl bodies which many of them contain. These cells are apt to be mistaken for the ova of parasites. _Starch-granules_ sometimes retain their original form, but are ordinarily not to be recognized except by their staining reaction. They strike a blue color with Lugol's solution when undigested; a red color, when slightly digested. _Muscle-fibers_ are yellow, and sometimes appear as short, {241} transversely striated cylinders with rather squarely broken ends. Generally, the ends are rounded and the striations faint, or only irregularly round or oval yellow masses are found. _Curds of milk_ are especially important in the stools of children. They must be distinguished from small masses of _fat_. The latter are soluble in ether, and stain red with Sudan III. Excess of any of these structures may result from excessive ingestion or deficient intestinal digestion.