_Symptoms._ This disease may be present in a poultry yard for some time without being detected. Suspicion should be aroused if birds gradually lose weight and die. If a bird that has gradually been getting thinner, goes lame, or loses the use of a wing, without apparent injury, the evidence that tuberculosis is present is strong, but positive proof of its presence can be obtained only by post-mortem and microscopic examination. This disease generally attacks adult birds. [Illustration: FIG. 24.—ORGANS AFFECTED BY TUBERCULOSIS AND BLACKHEAD _a._ Normal spleen. _b._ Tubercular spleen. _c._ Portion of tubercular liver. _d._ Blackhead liver of turkey for comparison with _c_. _a_ and _b_ after Edwards.] _Cause._ The specific organism causing this disease, known as the _Bacillus tuberculosis_ (Fig. 5), infects the liver (Fig. 24), the spleen (Fig. 24), and other organs, least frequently the lungs. The disease may be introduced into a flock by the purchase of an infected bird, and may be spread by uninfected birds picking up the excrement of diseased birds with their food. _Treatment._ There is no known cure. The insidious manner in which this disease advances through a poultry yard makes it a very serious malady. Birds suffering from it should be killed and burnt. Thorough disinfection of coops, etc., should be made. Strict attention to sanitation will help in preventing and controlling this disease. If many birds in a flock are believed to have tuberculosis, it would be well to destroy the whole flock and start again, preferably on fresh ground. WHITE DIARRHEA OF CHICKENS _A very serious disease, causing the death of large numbers_ _Symptoms._ Chickens are generally attacked when 10 to 15 days old. They appear listless, their feathers become rough, and they stand about with drooping wings. A white diarrhea is soon noticed. Chicken after chicken shows similar symptoms and dies, resulting in much loss and discouragement to the poultry rearer. [Illustration: FIG. 25.—CHICKENS AFFECTED WITH WHITE DIARRHEA Ten-day White Leghorn chickens showing symptoms of bacillary white diarrhea. (After Rettger & Stoneburn.)] [Illustration: FIG. 26.—HEALTHY CHICKENS Normal ten-day White Leghorn chickens. (After Rettger & Stoneburn.)] _Cause._ Various causes, such as improper or stale food, may upset the chicken’s digestive organs and give rise to a whitish diarrhea, but the term “white diarrhea” is best restricted to a contagious form of diarrhea due to minute parasites in the intestinal tracts of chickens. A coccidium and a bacillus have been proved by different investigators to cause very similar forms of white diarrhea. A distinct form of white diarrhea, known as brooder pneumonia, is described on page 35.