250 THE HORSE IN HEALTH AND DISEASE 



The disease is occasionally seen in the horse, but cattle and 

 hogs are much oftener affected. In some herds of cattle as high as 

 80 per cent, of the animals have been found infected. 



This malady is caused by the tubercle bacillus discovered by 

 Robert Koch in 1882. The organism is extremely small and 

 belongs to the acid-fast group. It is difficult to isolate directly 

 from the tissues. On artificial media it grows slowly. 



Infection is usually acquired by eating food or drinking water 

 that has been contaminated by discharges from tubercular animals. 

 Lesions of the disease appear first in the digestive organs. Later, 

 the blood-stream may carry the bacilli to the lungs and other 

 parts of the body where secondary foci of infection develop. 



The symptoms of equine tuberculosis are similar to those ex- 

 hibited by other classes of animals suffering from the chronic form 

 of the disease. One of the commonest features is a gradual 

 wasting away. This is followed by death after a period of months 

 or som.etimes years of ill-health. The history often points to the 

 disease having set in after an attack of influenza. When confined 

 to the lungs a cough and some difficulty in breathing occur and 

 may be the only signs noticeable for many weeks. If the intestines 

 are infected, digestive disturbances are present and absorption is 

 interfered with. Chronic, persistent diarrhea is a marked symp- 

 tom in advanced cases. 



A biologic test is used to determine the presence of infection. 

 It consists of injecting tubercuUn, a solution of the products of 

 the tubercle bacilli, into the body of the suspect. If the animal 

 is infected, a rise of temperature of more than 2° F. occurs a few 

 hours after the injection. The tuberculin test is recognized as a 

 refiable method of diagnosis. It is not infallible or fool-proof, but 

 is much more satisfactory than a diagnosis based entirely on a 

 physical examination. Horses with a temperature higher than 

 101.5° F. should not be tested. The dose of tuberculin is similar 

 to that employed for cattle, viz., 2 c.c. per 1000 pounds of weight. 

 A firm swelling nearly always appears at the point where the tuber- 

 culin was injected if the horse is tuberculous. It disappears in 

 from eighteen to twenty-four hours. 



