316 VETERINARY BACTERIOLOGY 



and may even recover. The avian type ordinarily does not pro- 

 duce fatal infection in guinea-pigs, although rabbits succumb and 

 fowls and pigeons contract the disease readily. 



Character of Disease and Lesions Produced. Almost any part 

 of the body may be affected with tuberculosis. The disease, 

 wherever found, generally involves the lymphatics. It is charac- 

 terized by the development of nodules having an essentially similar 

 structure in all tissues. The presence of the tubercle bacilli in a 

 tissue causes a proliferation of the fixed connective-tissue cells to 

 form the beginning of a miliary tubercle. Lymphocytes are gener- 

 ally attracted and are present in the surrounding tissues in con- 

 siderable numbers. A more or less definite layer of " epithelioid " 

 cells forms the boundary of the tubercle. Typical giant-cells 

 with peripheral nuclei are found near the center. Coagulation 

 necrosis proceeds and the interior caseates. Encapsulation with 

 fibrous tissue may occur, and the whole may eventually become 

 calcified. These calcareous grains persist in healed tuberculous 

 areas. Tubercles frequently are formed in masses. In the cow 

 tubercular lymph-glands sometimes become as large or larger than 

 an orange. 



The arrangement of the nodules frequently shows clearly the 

 path of the spread of the bacilli through lymphatic metastases. 

 Direct growth through tissues with invasion of new areas probably 

 rarely occurs. The organisms are not commonly found in the 

 blood-stream, although they may sometimes be carried to other 

 parts of the body by this means. Infection of the bones, joints, 

 and meninges probably occurs in this manner. 



The organs most commonly the seat of lesions vary with the 

 species of animal and the mode of infection. In the human, pul- 

 monary infection (consumption) is most common, although in- 

 testinal tuberculosis, infection of the lymphatics of the neck 

 (scrofula) , of the bones and joints (tubercular osteitis and arthritis), 

 of the meninges, and of the liver, spleen, kidneys, and other organs 

 of the body and the serous membranes lining the cavities, are not 

 uncommon. Lupus or tuberculosis of the skin is of frequent 

 occurrence in certain European countries. Cattle generally show 

 nodules in the mesentery and in the peritoneum (Perlsucht or 

 pearl disease). The lungs and the accompanying lymph-glands 



