578 VETEEINAEY HYGIENE 



losis of the udder is not employed. Its expense would not 

 appear to be great, and if universally adopted would in a 

 marked degree lower the proportion of tuberculous animals 

 in the United Kingdom, and open the road in course of 

 years to the final extinction of the disease by compensation. 



So widespread is tuberculosis amongst our herds, that 

 measures of extermination must be gradual unless the 

 country wishes to be involved in a ruinous expenditure. 



So far as we at present know, it is probable that on the 

 average at least one quarter of our cattle are affected, and 

 one third of our milch cows. In individual herds it may 

 vary from 7 per cent, to 50 per cent. Not so far from our 

 own door, viz., in the Channel Islands, tuberculosis is very 

 rare ; in our possessions in South Africa it is practically 

 unknown. 



For all practical purposes tuberculosis may be considered 

 a disease of the bovine ; both horses, swine, and sheep, 

 suffer, but the latter so rarely that only two or three cases 

 have been recorded amongst British sheep, though on the 

 authority of McFadyean there is no difficulty in infecting 

 the animal experimentally.* Horses, according to the 

 same observer, suffer more frequently than is supposed. 

 Pigs are commonly affected. 



Tuberculin Testing. — The testing of animals for tuber- 

 culosis by means of tuberculin has enormously reduced 

 our previous difficulties in diagnosis. We can now pick 

 out with considerable accuracy nearly all tuberculous 

 animals. A possibility of error does exist, even when the 

 operator has immense experience, but the margin of error 

 in expert hands is small, and in dealing with such a 

 disease as tuberculosis is negligible. It is hardly necessary 

 to add that the tuberculin used should be above suspicion, 

 and that the syringe employed should be in thorough 

 working order so that the full dose may be injected. 



The defects in the method are that an animal may not 

 react until some time after infection, and that an advanced 

 case may not give a distinct reaction. This latter is not so 



* Journ. Comp. Path, amd Therap., vol. xv., part ii., p. 103, 1902. 



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