The animals should be killed at the end of six or eight weeks, if they do not die before that time, and a careful postmortem examination should be made for the characteristic pearly-gray or yellow tubercles scattered over the peritoneum and through the abdominal organs, particularly the spleen, and for caseous inguinal and retroperitoneal lymph-glands. The tubercles and portions of the caseous glands should be crushed between two slides, dried, and stained for tubercle bacilli. The bacilli are difficult to find in the caseous material. THE MOUTH Micro-organisms are always present in large numbers. Among these is _Leptothrix buccalis_ (Fig. 121), which is especially abundant in the crypts of the tonsils and the {271} tartar of the teeth. The whitish patches of _pharyngomycosis leptothrica_ are largely composed of these fungi. They are slender, segmented threads, which generally, but not always, stain violet with Lugol's solution, and are readily seen with a one-sixth objective. At times they are observed in the sputum and stomach fluid. In the former they might be mistaken for elastic fibers; in the latter, for Boas-Oppler bacilli. In either case, the reaction with iodin will distinguish them. [Illustration: FIG. 121.--Gingival deposit (unstained): _a_, Squamous epithelial cells; _b_, leukocytes; _c_, bacteria; _d_, Leptothrix buccalis (Jakob).] Thrush is a disease of the mouth seen most often in children, and characterized by the presence of white patches upon the mucous membrane. It is caused by the thrush fungus, _Oïdium albicans_. When a bit from one of the patches is pressed out between a slide and cover and examined with a one-sixth objective, the fungus is seen to consist of a network of branching segmented hyphæ with numerous spores, both within the hyphæ and in the meshes between them (Fig. 122). The meshes also contain leukocytes, epithelial cells, and granular débris. {272} [Illustration: FIG. 122.--Thrush fungus (Oïdium albicans) (Jakob).] [Illustration: FIG. 123.--Bacillus diphtheriæ, from culture on blood-serum. X1000 (Fränkel and Pfeiffer).] Acute pseudomembranous inflammations, which occur chiefly upon the tonsils and nasopharynx, are generally caused by the diphtheria bacillus, but may result from streptococcic infection. In many cases diphtheria {273} bacilli can be demonstrated in smears made from the membrane and stained with Löffler's methylene-blue or 2 per cent. aqueous solution of methyl-green. They are straight or curved rods, which vary markedly in size and outline, and stain very irregularly (Fig. 123). A characteristic form is a palely tinted rod with several deeply stained granules (metachromatic bodies), or with one such granule at each end. They stain by Gram's method. It is generally necessary, and always safer, to make a culture upon blood-serum, incubate for twelve hours, and examine smears from the growth.