POST-MORTEM LESIONS.--The effect of the tubercle bacillus on the body is to irritate and destroy the tissues. Lumps or tubercles form in the lymphatic glands, liver, lungs, spleen (Fig. 90), serous membranes, kidneys and other body organs (Figs. 91 and 92). The tubercles may be very small at first, but as the disease progresses they continue to enlarge until finally a tubercular mass the size of a base-ball, or larger, is formed (Figs. 93, 94, 95 and 96). Lymphatic glands may become several times larger than normal and the liver and lungs greatly enlarged. The pleura and peritoneum may be thickened and covered with tubercles about the size of a millet seed, or larger. Pleural and peritoneal adhesions to the organs within the body cavities are common. [Illustration: FIG. 91.--The carcass of a tubercular cow. Note the condition of the carcass, and the tubercular nodules on the chest wall, showing that the disease was well advanced.] [Illustration: FIG. 92.--A section of the chest wall of a tubercular cow showing a better view of the diseased tissue.] The tubercle usually undergoes a cheesy degeneration. Old tubercles may become hard and calcareous. Sometimes the capsule of the tubercle is filled with pus. A yellowish, cheesy material within the capsule of the tubercular nodule or mass is typical of the disease. THE TUBERCULIN TEST.--The only certain method of recognizing tuberculosis is by this test. There is no other method of recognizing this disease that is more accurate than the above test. The substance used in testing animals for tuberculosis is a laboratory product. It is a germ-free fluid prepared by growing the tubercle bacillus in culture medium (bouillon) until charged with the toxic products of their growth. The culture medium is then heated to a boiling temperature in order to destroy the germs. It is then passed through a porcelain filter that removes the dead germs. The remaining fluid is tuberculin. [Illustration: FIG. 93.--A very large tubercular gland that had broken down in the central portion.] _There are two methods of applying_ the tuberculin test. The subcutaneous test consists in injecting a certain quantity of tuberculin beneath the skin, and keeping a record of the body temperature of the animal between the eighth and eighteenth hours following the injection. Tubercular animals show an elevation in temperature that comes on about the eighth or twelfth hour of the test. In the _intradermal test_, a small quantity of a special tuberculin is injected into the deeper layer of the skin. The seat of the injection in cattle is a fold of the skin on the under side of the base of the tail. In tubercular animals the injection is followed by a characteristic local swelling. [Illustration: FIG. 94.--A tubercular gland that is split open.] [Illustration: FIG. 95.--Caul showing tuberculosis.] [Illustration: FIG. 96.--Foot of hog showing tuberculosis of joint.]