The anatomical changes in bovine tubercle are mostly found in the lungs and their membranes, the pleuræ. It also affects the internal membrane lining, the abdomen and its chief organs, the peritoneum, and the lymphatic glands. In both these localities a characteristic condition is set up by small grey nodules appearing, which increase in size, giving an appearance of "grapes." Hence the condition is called grape disease, or _Perlsucht_. The organs, as we have said, are equally affected, and when we add the lymphatic glands we have a fairly complete summary of the form of the disease as it occurs in cattle. As has been clearly pointed out by Martin, Woodhead, and others in their evidence before the Royal Commission, the organs, glands, and membranes are the sites for tubercle, not the muscles (or "meat"). This latter is most liable to convey infection when the butcher smears it with the knife which he has used to remove tubercular organs.
As regards the udder in its relation to milk infection, it may be desirable to state that the initial lesion, according to Nocard and Bang, takes the form of a progressive sclerosis. The interlobular connective tissue, normally scanty, becomes thickened, fibrous, and infiltrated by minute miliary granulations. The granular tissue is thus "smothered by the hypertrophy and fibrous transformation of the interstitial connective tissue" (Nocard). The walls of the ducts are thickened and infiltrated, the lumen frequently dilated by masses of yellow caseous material. On the whole it may be said that tubercle of the udder is rare. Usually only one quarter is attacked, and by preference the posterior. For some time the milk remains normal, but gradually it becomes serous and yellow, and contains coagula holding numbers of bacilli. Lastly, it becomes purulent and dries up altogether. While the milk is undergoing these changes the lesion of the udder is becoming more marked, the tissue becomes less supple, and the toughness increases almost to a wooden hardness.
The general anatomical characteristics of the disease are similar to those occurring in man.
The percentage of cattle suffering from tubercle varies. In Germany it appears to vary from 2 to 8 per cent. of all cattle, in Saxony 17 to 30 per cent., in England 22 per cent. approximately (in London 40 per cent.), in France 25 per cent. Lowland breeds are much more infected than mountain breeds, which possess stronger constitutions.