METASTASIS IN TUBERCULOSIS. 587 



that of metastasis by way of the lymph channels. 

 When bacilli penetrate a surface, with or without 

 the formation of a lesion at the point of entrance, 

 as in the mouth cavity, intestinal canal, or bron- 

 chial surface, they are carried to the lymph glands 

 of the region in which the tuberculous process is 

 instituted. As in plague, the infection atrium at 

 times is indicated by the set of glands which is in- 

 volved. In certain localities the secondary invasion 

 of other structures takes place directly without the 

 intermediate involvement of lymph glands, as in 

 tuberculous meningitis caused by extension from 

 the middle ear, and tuberculous peritonitis or peri- 

 carditis by extension from the pleura, Very fre- 

 quently tuberculosis of the lymph glands and other 

 tissues heals spontaneously, as described below. 

 In case healing does not occur, metastases con- 

 tinue from one lymph gland to another and to new 

 sets of glands until the larger lymph channels are 

 reached, as a consequence of which extensive re- 

 localization of a focus often causes a wide depart- 

 gional or general tuberculosis results. Accidental 

 localization of a focus often causes a wide depart- 

 ure from the slow development just described. Not 

 infrequently tuberculosis in a lymph gland, which 

 is contiguous to a large lymph channel, as the tho- 

 racic duct, invades the wall of the latter, the sur- 

 face softens from caseation or liquefaction and the 

 contents, impregnated with countless bacilli, are 

 gradually thrown into the circulation. Miliary 

 tuberculosis, first of the lungs and then of other 

 tissues, through the arterial circulation, follows 

 such an accident. A similar course with variations 

 in localization, follows invasion of the walls of 

 branches of the pulmonary artery or vein. Eup- 

 ture of a focus into a bronchus is followed by re- 



