rWAGNOSlS OP BOVINE TUBEHCULOSlS 347 



than normal over the upper half of the chest, and is particularly 

 marked during expiration. Usually the superficial glands in the throat, 

 those between the jaws, and under the ear or of the udder are swollen 

 and hard. The animal may continue for months in an apparently 

 healthy condition. When the disease is abdominal and the glands 

 and organs in the belly are chiefly affected, the symptoms of defective 

 nutrition are early evident, namely, emaciation, lessened milk secre- 

 tion, indigestion, breathlessness, and more or less rapid failure in 

 general health. In these cases the udder should be especially 

 examined. 



It should be noted that clinical diagnosis of tuberculosis, especi- 

 ally of udder tuberculosis, does not enable us to judge whether 

 tubercle bacilli are secreted along with the milk of the cow in 

 question. The bacteriological test and tuberculin are necessary. 

 The former is sometimes tedious, and the latter remains at present 

 our only quick and sure method. 



(&) Bacteriological Examination. — This method of diagnosis can 

 be applied at once in suspected udder disease by examination of the 

 milk ; or, as recommended by Nocard, a trocher may be used by 

 which a small fragment of tissue from the indurated portion of the 

 udder may be obtained for examination. Mucus or discharges from 

 throat, wounds, and ulcers may also be examined and assist in 

 diagnosis. The only sure method of bacteriological examination is 

 by inoculation of animals. Microscopical and cultural tests are 

 unreliable. 



(c) Tuberculin. — In recent years the method of testing herds for 

 tuberculosis by means of tuberculin has come into vogue, and it will 

 be necessary to refer briefly to this subject. The discovery by Koch, 

 in 1890, of the production of fever, indicated by a rise in tempera- 

 ture, in tuberculous animals into which he injected a sterilised 

 glycerine extract of pure cultures of tubercle bacilli, while it 

 produced no effect whatever when the animals were free from that 

 disease, furnished us with a simple but fairly reliable diagnostic 

 agent. 



Tuberculin is a soluble product of cultures of tubercle bacilli, of 

 which a glycerine extract is made, which is sterilised by heat and 

 filtered through porcelain, so that it contains no living germs, and 

 therefore cannot produce tuberculosis in animals injected with it. 

 It has, therefore, no effect on healthy animals ; in some cases the 

 disease is aggravated by it when it exists, but it cannot be produced 

 by it. The lymph must not be exposed to sunlight ; it must not be 

 frozen, and must be kept well corked to exclude air. 



Koch's "old tuberculin" is made from glycerine-veal broth 

 cultures of B. tuberculosis by means of evaporation and precipitation 

 with alcohol. The liquid cultures are thus concentrated to one-tenth 



