94 MASTITIS OF THE COW 



vein wall usually induces a thrombotic process, however, 

 which, as a rule, prevents infection of the blood. Ulcera- 

 tion finally occurs, however, in the larger veins which are 

 not occluded by the thrombus. In this case the thrombus 

 is broken up by the softened tuberculous necrosis which is 

 ultimately emptied into the blood stream. In this way a 

 secondary blood-infection is produced which metastasizes 

 to the lungs. 



Blood-infection in consequence of this tlirombotic proc- 

 ess always occurs later and on a smaller scale than the milk- 

 infection described. 



Great numbers of such venous thrombi cause venous 

 stasis with subsequent transudation by which the oedema, 

 which has already been caused by lymph stasis, is increased. 



Arterial walls may be destroyed in the same manner, 

 following which the condition may be more widely dis- 

 tributed by infection of the arterial blood. 



Tuberculous Wounds. — If the tuberculous lesions lie 

 near the skin, they may ultimately cause its necrosis and 

 the softened tuberculous necrotic substance may be dis- 

 charged from the wound so formed. This is somewhat 

 rare. 



If the tuberculous processes lie adjacent to a primary 

 wound or a secondary wound produced by ulceration, the 

 tuberculous processes may ulcerate into these wounds. 



Types. — Depending upon the ports of infection, as in 

 pyobacillosis, the following forms of udder-tuberculosis are 

 distinguished: (1) primary udder- tuberculosis ; (a) by in- 

 fection through the teat canal; (b) by infection through 

 wounds ; ( 2 ) secondary or embolic udder-tuberculosis. 



These types have the same differential characteristics 

 in general as the forms of pyobacillosis described. 



Primary udder-tuberculosis following teat infection is 

 comparatively rare. Of 137 cows which had udder-tuber- 

 ciilosis, slaughtered at the expense of the state, nine, or 



