The structural changes which are met with depend very much upon the organ which is affected. In the lungs there are sometimes found miliary tubercles, while in other cases masses of deposit an inch or more in diameter are met with. These larger masses contain a quantity of soft yellow material in the centre. The bronchial lymphatic glands, and also the glands in other parts of the body, are sometimes enormously enlarged, and present yellow softened masses in their interior, and occasionally patches of calcareous or earthy deposit.
On the lining membranes of the chest and belly isolated tuberculous, patches are met with, but the grapy form, as it is called, which is so common in cattle, is not often seen in the horse. Cases of tuberculous deposit in the bones have been recorded, and are probably more common than is generally supposed, the fact being that cases of disease of the bones in the horse are commonly classed under the head of caries or necrosis, and the diseased structures are not submitted to any critical examination for the detection of the tubercle bacilli.