352 VKTKKIXARV PATHOL(.)GV. 



Sometimes there is a combination of both conditions and occa- 

 sionally the tul)ercles contain calcareous i^ranules. The central 

 portion of porcine tubercles rarely contains li<iuefied necrotic 

 tissue; 



Alicroscopicallv porcine tubercular lesions are always cellular 

 in the beginning. The cellular tubercles are fairly constant in 

 structure regardless of the tissue in which they occur. The 

 center i^ at tirst represented b}- a mass of lymphoid cells, the 

 other cellular elements occurring as the tubercle develops. 



Xecrosis, or fibrosis, succeeds the cellular siage in the por- 

 cine tubercular lesion. Necrosis of tubercles is probably the 

 result of the activity of very virulent bacteria or the low resis- 

 tance, of the infected animal. The necrotic center may be sur- 

 rounded bv a cellular zone (lymphoid and endothelial cells), or 

 it mav be surrounded by fibroblasts. The necrotic material is 

 invariablv caseatcd and later becomes calcified. 



Fibrous lesions varv from the formation of small quantities 

 of fibrous tissue to dense filjrous centers. Fibrous lesions are 

 probaljlv produced by bacteria of low \-irulence, or occur in ani- 

 mals ha\ing a marked resistance. The central portion of the 

 fibmus lesion mav Ijecome calcified. 



The S(i-callcfl arbor vitae gland is a fibrr)us center in which 

 the fil)rous tis-^ue is arranged similar to the trunk and branches 

 of a tree, hence the name. This lesion is oljserved in the hog 

 in the cervical lymph nodes. The bacterium tuberculosis has 

 been denninstrated in about 30 per cent of arbor \'itae glands. 



The lesions of porcine tuberculosis are in brief either cellu- 

 lar, necrotic and calcified tul)ercles, or cellular, fibrous and calci- 

 fied tubercles. The lesion is always non-vascular as in other 

 animals. 



A7'iaii tubercular lesions are very similar to mammalian tubercles, 

 and ma\- occur in practicallv anv tissue. iMicroscopically, avian 

 tuljercules are found to contain giant cells, endothelioid cells, 

 small round cells and connecti\'e tissue cells, the arrangement of 

 wh'ch is the same as descrilied in mammalian tubjercles. Avian 

 tubercular lesions have been found in the liver, spleen, intestine, 

 mesenter\-, kidncA", lung, skin, and bones, the frequency being 

 in the rirder mentioned. 



A\ian tubercles in glandular tissue, i. e., in the liver, kidney, 

 snleen, etc., begin as small, dirty, white cellular foci, Thev usu- 

 alh- ricctir sinjdv, though thcA- maA- occasionallv l)ecome conflu- 

 ent, thus producing nodules a quarter of an inch in diameter. 

 As the tuliercles in glandular tissue tindergo necrosis, they as- 

 sume a yellowish color. Intestinal tubercles are about the same 



