336 TUBERCULOSIS AS A TYPE OF BACTERIAL DISEASE 



bacilli are readily found, and whether that be so or not the milk is 

 highly infective.* 



The Entrance of the Bacillus into Milk. — There are two main 

 sources of the tubercle bacilli found in milk, namely, a bovine source 

 and a human source. The two common channels respectively are a 

 tuberculous udder and' a phthisical lung. From the former, milk 

 may derive a direct and abundant supply of tubercle bacilli ; from 

 the latter, milk may become indirectly contaminated by the parti- 

 culate matter of dried sputum. 



Tuberculosis may be introduced into healthy cows in a variety of 

 ways. The most common method is by means of a tuberculous 

 animal, from the excretions and discharges of which infection may 

 be conveyed to soil, water, air, fodder, and general surroundings. In 

 this way not only other animals cohabiting with a tuberculous 

 animal become infected, but premises, stables, and utensils may also 

 become infected. The milk of a tuberculous animal may also be 

 consumed by other animals on the farm, and so a vicious circle of 

 infection is. completed. Eavenel has shown that by the cough of a 

 tuberculous cow tubercle bacilli may be distributed. Of thirty-four 

 examinations carried out on five tuberculous cows, tubercle bacilli 

 were detected on twenty occasions. One of the cows constantly 

 coughed up a tenacious mucus containing large numbers of tubercle 

 bacillLf The saliva as well as the bronchial mucus of tuberculous 

 cows has been found to contain abundant bacilli, and by licking her 

 udder it is possible for a tuberculous cow to convey tubercle bacilli 

 to its exterior surface. 



The excreta also are infective when lesions are located in the 

 alimentary canal. In tuberculosis affecting the alimentary canal of 

 the cow (1 per cent, of the cases), it is thus possible to get contam- 

 ination of the milk, indirectly, from the excreta. The mucous 

 membrane of the intestine, especially the colon, sometimes shows 

 tubercular ulcers, which are less frequently observed in the abomasum. 

 Tubercles may also develop under the mucous membrane, and serosa 

 of the stomach and intestines. In these ways arises a condition of 

 intestinal tuberculosis, which in its acute or ulcerating stage will 

 cause the excreta to be loaded with tubercle bacilli. Any one 

 familiar with a cowshed will at once recognise how readily milk 

 might become infected under such circumstances, which, though 

 undoubtedly exceptional, must not be overlooked.^ In these ways 

 stalls may become infected and transmit the disease to fresh herds 

 stabled in such premises. Nor are herds unstabled always free from 



* See also Report of Royal Commission on Tuberculosis, 1896, part iii., p. 142. 

 t Commonwealth of Pennsylvania, Bulletin 75 (Pearson and Ravenel), 1901, p. 82. 

 X Trans. British Congress on Tuberculosis, 1901, vol. iii., p. 664 (Boinet and 

 Heron). 



