UDDER-TUBERCULOSIS 91 



tubercles be produced. This is local metastasis or extension 

 by leucocytes. 



In this manner the organisms can gain entrance to the 

 lymph- vessels and be carried to the supramammary lymph- 

 glands, where the degenerated leucocytes are retained and 

 a tubercle is produced. Thus tuberculosis of the lymph- 

 glands depends upon infection of the lymph and the process 

 is therefore called lymphogenous metastasis. 



Tuberculosis in the lymph-glands following such lym- 

 phatic metastasis is more recent than the tuberculosis of the 

 udder. Thus we may have distinct caseation in the udder, 

 but subsequent caseation in the lymph-glands may fre- 

 quently be so insignificant that it is not visible to the naked 

 eye. 



From these lymph-glands leucocytes may carry the or- 

 ganisms through the lymph to the lumbar-glands and from 

 here by way of the thoracic duct to the blood stream, by 

 which it may finally be widely distributed. Thus lymphog- 

 enous metastasis may be transformed into hsematogenous 

 metastasis. 



Besides these forms of metastasis it may also be trans- 

 ported through milk [galactogenous metastasis] and blood, 

 which will be discussed in another chapter. 



Development of the Tubercle. — The primary tu- 

 bercle manifests slow development. Central necrosis pro- 

 gresses gradually. During the lactation period, however, 

 the tubercle develops somewhat rapidly in the succulent 

 stroma while it develops very slowly in the alactiferous 

 udder. 



Adjacent primary tubercles may coalesce by extension. 

 Their connective-tissue walls and cellular zones join first 

 and finally the necrotic centres coalesce and form a large 

 area of necrosis surrounded by a wider zone of lymphocytes 

 and connective tissue. By coalescence of a large number 



