134 MILK AND THE PUBLIC HEALTH chap. 



tubercle bacilli may exist in such a state as would be impossible 

 of diagnosis by this means." 



In view of the stress which has been laid by some writers 

 upon the sufficiency of systematic veterinary inspection to 

 safeguard the purity of milk, it is very important to recognise 

 that the diagnosis of early tuberculosis of the udder is often 

 extremely difficult. For example, Dewar says:^ "In the 

 udder the progress of the disease is often slow, and there 

 is no doubt but it may exist for weeks in such a condition 

 as to render the milk dangerous before the most expert 

 clinician could detect its presence." Nocard ^ remarks 

 that the diagnosis of tuberculous mammitis is " both urgent 

 and difficult ; the clinical symptoms are vague, and generally 

 point to a range of probabilities which are more or less 

 certain. Even if the cow has reacted to tuberculin, it does 

 not necessarily follow that the induration of its udder is 

 tuberculous, for tuberculous cows, as well as healthy ones, are 

 liable to contract mammitis of various natures." 



Bacteriological Examination. — The utility of this method 

 will depend upon the nature of the tuberculosis with which 

 the animal is affected. In " closed " tuberculosis, of the 

 glands for example, direct bacteriological examination is of no 

 assistance. For " open " tuberculosis, by which is meant 

 tuberculosis of organs communicating with the exterior, 

 whereby tubercle bacilli are discharged outside the animal 

 body, bacteriological examination of the vaginal secretion, 

 faeces, etc., may be of marked diagnostic value. This method 

 is of fundamental assistance in the diagnosis of udder tuber- 

 culosis, and this variety of the disease can be diagnosed with 

 great certainty by bacteriological examination of the milk 

 (drawn off without contamination) and injection into guinea- 

 pigs. 



The diagnosis of tuberculosis by the agglutination test 

 has been introduced by Arloing, but the practical difficulties 

 are considerable, and the method has not been adopted as one 

 of wide applicability. 



By the Use of Tuberculin. — Tuberculin (Koch's old tuber- 

 culin) is prepared by growing tubercle bacilli in glycerine veal 



' Trans. British Congress on Tuberculosis, 1901, vol. iv. p. 3. 

 2 Ibid. p. 8. 



