590 Tuberculosis. 



other causes in tuberculosis of that organ, the milk retains its 

 normal appearance for a long period. When in the later stages 

 changes do occur in the physical appearance of the milk, they 

 are characterized by the absence of pus and mucus (sliminess). 

 Irregular nodules in the tissue of one or more quarters of the 

 udder and enlargement of the super mammary glands indicate 

 the tuberculous nature of the affection. Actinomycosis and 

 botriomycosis produce similar swellings in the tissue of the 

 udder but are apt to be firmly adherent to the overlying skin, 

 they frequently break open and discharge their contents, and 

 the mammary glands are unaffected or only slightly and evenly 

 enlarged. In inflammation of the udder caused by streptococcus 

 infection the firm swelling bears a close connection with the 

 indurated base . of the teat while tuberculous disease usually 

 occurs higher up in the tissue of the udder. In the former 

 case also the milk is purulent from the beginning, and while 

 the mammary lymph glands may be swollen or enlarged they 

 are never irregular or nodular in form. Finally, the secretion 

 of the udder contains streptococci. Milk cysts may be differ- 

 entiated from tuberculosis by their elastic consistency. A 

 definite diagnosis of tuberculosis of the udder, especially in the 

 less pronounced cases, cannot be made without a bacteriologi- 

 cal examination and demonstration of the tubercle bacilli in 

 the milk (see p. 558) or in the tissue of the udder (p. 570). 



For the anatomical diagnosis of tuberculous processes the 

 presence of small gray transparent or yellowish, firm nodules 

 (tubercles), which usually occur either exclusively within or 

 in the neighborhood of cheesy foci and ulcers may be accepted 

 as definite evidence. Accepting this as a basis, other processes 

 that resemble tuberculosis (actinomycosis, botriomycosis, 

 caseated parasitic nodules, chronic inflammations of the lungs, 

 etc.) are easily differentiated from tuberculosis. In all cases, 

 however, the demonstration of the tubercle bacillus is necessary 

 as final evidence of the tuberculous nature of any morbid product 

 or tissue. 



Prognosis. Local morbid processes brought about by nat- 

 ural infection may, under favorable conditions, not infrequently 

 remain restricted to a definite area or end in recovery through 

 an inflammatory reaction in the surrounding tissue. Healthy 

 adult animals are almost always met with even in badly infected 

 herds and it seems that their condition of health is due, not 

 to a natural individual immunity but rather to repeated infec- 

 tion with tuberculosis followed by recovery and consequent im- 

 munity to later infections. The encapsuled and calcified cheesy 

 foci which are not infrequently met with on inspection of 

 slaughtered animals, in certain organs, especially lymph glands, 

 point to such a favorable course of local infections. The results 

 of tuberculin tests, especially in the case of young animals fre- 

 quently point to this possibility, as in certain cases where the 



