404 t CHRONIC INFECTIOUS DISEASES 



catarrhal conjunctivitis) may occur in healthy individuals, 

 especially where full strength tuberculin has been used. 

 Further, in healthy cattle the application of this test at spaced 

 intervals will often induce an apparent reaction which is 

 very confusing. Sometimes tuberculous cattle will not react. 

 Negative results, therefore, are not decisive. 



(c) The cutaneous applications of tuberculin consists in 

 either rubbing the tuberculin (a) into the intact (shaved 

 and cleaned) skin (dermic), (b) painting it upon the scarified 

 skin (endermic) or (c) injecting it into the substance of the 

 skin (intradermic), probably best into one of the skin folds 

 extending from the tail-root (tail elevated) on each side 

 downward to' the anus. In tuberculous cattle the positive 

 reaction, modified somewhat by the method of application, 

 consists in an inflammatory (edematous) swelling which 

 usually appears within twenty-four hours and often lasts 

 for two or three days. When the skin has been scarified, 

 small vesicles sometimes appear. While the dermal appli- 

 cation of tuberculin may furnish valuable contributory 

 evidence in detecting tuberculosis, it is often not conclusive 

 enough to be relied on. Negative results are not always 

 indicative of the absence of tuberculosis. However, this 

 method of applying tuberculin is still in the experimental 

 stage. 



2. Microscopic Determination of Tubercle Bacilli in the Secre- 

 tions and Excretions or in Tissue from the Suspected Patient. — 

 While in man the examination of sputum for tubercle bacilli 

 is commonly practised, in animals, which do not spit, the 

 method is not so feasible. However, milk, manure, urine, 

 and tissue (portion of abscess walls, udder, superficial lymph 

 glands, tuberculous growths, etc.), may be subjected to 

 microscopic examination for tubercle bacilli. Of late bron- 

 chial slime collected with special devices from the gullet 

 (gullet dipper) and trachea (tracheotomy tube, wire carrying 

 sterile gauze at end) has been used. In cattle this method 

 has proved of service in detecting open cases. In this con- 

 nection it should be borne in mind that there are many 

 other bacilli which are "acid-fast," and so closely resemble 

 the tubercle bacilli morphologically and in staining properties 



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