MUNICIPAL HYGIENE 689 



the milk. He little realizes that ia a case of indolent, gradually 

 extending induration of the udder, the fact that the mUk retains its 

 normal appearance for a time is a very grave symptom, and, to say the 

 least, very highly suspicious of the existence of tuberculosis of the 

 udder.' 



The essential feature in the sweUing of tuberculosis of 

 the udder is that, unlike other forms of mastitis, the gland 

 does not pass into the condition of atrophy, which so 

 commonly sets in after other disturbances, that of actino- 

 mycosis being, of course, an exception. The permanent 

 increase in size and density of the organ are symptoms of 

 supreme importance. 



This increase in size may, as we have previously noted, take 

 a few weeks, but before the gland shows any actual hard- 

 ening the milk may contain bacilli. It is not easy to see, 

 as matters at present stand, how the existence of disease 

 can be determined earlier, but it points to the necessity for 

 systematic inspection of the udders of all dairy stock, if 

 possible once a month, and at longest once in two months. 



A good deal has been written on the proportion of cattle 

 affected with tuberculosis, especially since the introduction 

 of tuberculin. McFadyean* regards 30 per cent, of the 

 cattle in Great Britain as tuberculous, but though tuber- 

 culous udders have been placed as high as 10 per cent., 

 this authority believes that 2 per cent, would be nearer the 

 truth. In this way he considers that as the average number 

 of cows in a dairy is under fifty, the majority of dairies and 

 farms supply milk free from tubercle bacilli. 



Both McFadyean and Nocard lay great stress on the 

 amount of dilution to which tuberculous milk may be 

 exposed. When the tuberculous milk is largely diluted by 

 mixing, as it would be in a big establishment, the danger 

 of infection is greatly reduced, whereas the milk from a 

 small establishment, and from single cows, may be most 

 highly infective. 



* ' Tubercle Bacilli in Cow's Milk a possible Source of Tuberculous 

 Disease in Man': Address to the British Congress on Tuberculosis, 



London, July, 1901. 



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