INFIXTIVE GRANULOMATA. 353 



size as those in olanduLar tissue. The intestinal lesions are usu- 

 ally quite hard and dense and present a ,t;-listeninj; appearance. 

 Necrosis frequently destroys the intestinal wall and thus a tuber- 

 cular intestinal ulcer is produced. Mesenteric tubercles are fre- 

 quently pedunculated and they nivariably present a pearl like 

 appearance. 



Extension. — Tuberculosis, except in some cases of the acute 

 f'lrm, essentially a localized disease. llo\ve\er, the di-ease, 

 even in the chronic form, has a tendency to extend and involve 

 new tissue. The extension ma_\- be accomplished l)y means of, 

 first, the lymphatic system, second, the digesti\-e, respiratory 

 and genito-urinary tubes, third, the blood vascular system and 

 fourth, by continuit\' and contii^uitv. 



Tuberculosis is usually extended by the lymphatic circulation. 

 Thus the first group of lymph nodes through which the h'mph 

 passes from a tubercular lesion is almost inxariably involved. In 

 fact this is a characteristic <.;f the disease. The large per cent of 

 lymphatic lesions is also evidence of extension b\- means of the 

 lymph. It has been pre\-iously stated that hogs are in\'ariably 

 infected by ingestion of tubercular material and in ii:! per cent of 

 tubercidar hogs the submaxillar\' lymph nodes are affected, which 

 is further evidence of h niphatic extension. The fact that infec- 

 tion ma^' extend along the digestive, respirator\- or geniti i-nrin- 

 ary tracts, has been demonstratefl. Thus the discharges, con- 

 taining the Bacterium tuberculosis from a pharyngeal tubercle 

 mav pass through the oesophagus and stomach and find a nidus 

 favorable for its development in the intestine. In a like manner 

 the lung tissue may become affected bv extension from laryngeal, 

 tracheal ov bronchial tuberculosis and prostatic tuberculosis may 

 result from extensi("in of renal tuberctilar lesions. In extensive 

 or generalized tuberculosis the tubercles not infrequently in- 

 volve and produce necrosis of the blood \-essel walls and tlie 

 \-irulentlv contamin.ated necrotic inaterial being discharged into 

 the blood resulting in tuberctdar metastasis. Thus tuf)ercMlosis 

 is extended b\' means of the blood. Extension by the fdood in- 

 variably results in generalized tuberculosis which is usually 

 acute. 



In the discussion of tubercular lesions, the formation of sec- 

 ondary and daughter tubercles was mentioned. The production 

 of secondary and daughter tubercles is a means of extension. 

 If the newly formed tubercles are in tl.c same kind of tissue as 

 the primary tubercle then the extension is by continuity. If the 

 secondary or daughter tubercles are in tissues dissimilar to that 



