196 BACTERIA 



turn to speak shortly of the outstanding facts of the chief 

 diseases carried by milk. 



Tuberculosis. It is well known that this disease is not a 

 rare one amongst cattle. The problem of infective milk is, 

 however, simplified at the outset by recognising the now 

 well-established fact that the milk of tuberculous cows is 

 only certainly able to produce tuberculosis in the consumers 

 when the tuberculous disease affects the udder. This is not 

 necessarily a condition of advanced tuberculosis. The udder 

 may become affected at a comparatively early stage. But 

 to make the milk infective the udder must be tubercular, 

 and milk from such an udder possesses a most extraordinary 

 degree of virulence. When the udder itself is thus the seat 

 of disease, not only the derived milk, but the skimmed 

 milk, butter-milk, and even butter, all contain tuberculous 

 material actively injurious if consumed. Furthermore, 

 tubercular disease of the udder spreads in extent and degree 

 with extreme rapidity. From these facts it will be obvious 

 that it is of first-rate importance to be able to diagnose udder 

 disease. This is not always possible in the early stage. The 

 signs upon which most reliance may be placed are the en- 

 largement of the lymph-glands lying above the posterior 

 region of the udder; the serous, yellowish milk which later 

 on discharges small coagula; the partial or total lack of 

 milk from one quarter of the udder (following upon excess- 

 ive secretion); the hard, diffuse nodular swelling and in- 

 duration of a part or the whole wall of the udder; and the 

 detection in the milk of tubercle bacilli. The whole organ 

 may increase in weight as well as size, and on post-mortem 

 examination show an increase of connective tissue, a num- 

 ber of large nodules of tubercle, and a scattering of small 

 granular bodies, known as " miliary " tubercles. Tuberculin 

 may be used as an additional test. The udder is affected 

 in about two per cent, of tuberculous cows. 



There are a variety of causes in addition to the vera causa, 



