Diagnosis. 569 



to recognize it with absolute positiveness. The symptoms 

 simply point, in a general way, to affection of certain organs, 

 but hardly enable us to form an opinion as to the nature of 

 the disturbance. Although the diagnosis is often suggested by 

 a suspicion of an infection, this of itself is not sufficient to justify 

 the positive diagnosis of tuberculosis. Symptoms pointing to 

 the existence of tuberculosis are as follows : Insidious develop- 

 ment of the disease, .gradual running down in condition, stunted 

 growth in young animals, periodical or occasional attacks of 

 fever without apparent cause and a gradually progressive af- 

 fection of the lungs. Great importance should be attributed 

 to enlargement of the lymphatic glands. While the latter may 

 occur as an independent affection it is usually an indication 

 of tuberculosis of the corresponding organs. On the other 

 hand enlarged lymph glands may, by exerting pressure on 

 neighboring organs, produce disturbances of function (bloating, 

 venous pulse, lameness) that would justify the conclusion that 

 deeper lying organs are affected. 



In the great majority of cases, however, an exact diagnosis 

 is possible only by the aid of special diagnostic methods, among 

 which microscopical examination of morbid tissues and secre- 

 tions, inoculation of experimental animals and the tuberculin 

 test are of practical importance. 



Post-mortem examination of slaughtered animals, or of 

 animals that died from the effects of the disease is usually 

 the easiest method of determining the tuberculous nature of 

 existing lesions, but even in such cases a microscopical examina- 

 tion is almost indispensable to enable us to differentiate with 

 certainty between tuberculosis and other morbid conditions 

 which occasionally show a remarkable similarity (actinomycosis, 

 pseudo-tuberculosis) . 



Microscopic Determination of Tubercle Bacilli. The determination 

 of true tubercle bacilli in a tissue or secretion absolutely clinches the 

 diagnosis of tuberculosis. Negative results of an examination for 

 tubercle bacilli do not, on the other hand, justify the exclusion of the 

 disease because tuberculous lesions, especially cheesy foci, may contain 

 very few tubercle bacilli. If tubercle bacilli are present in large 

 numbers, however, they are comparatively easy to demonstrate. But 

 in making a diagnosis it should always be kept in mind that there are 

 other bacteria with morphological and staining characteristics (acid-fast 

 bacteria) that give them a remarkable similarity to tubercle bacilli (see 

 p. 571). However, these acid- fast bacteria, except in paratuberculous 

 chronic enteritis of cattle, are not known to be pathogenic. They occur 

 merely as harmless saprophytes which have been carried from the 

 outside into exposed cavities and canals and their secretions. It is 

 only exceptionally that they are found in pathological tissues and thus 

 it is comparatively safe to regard all acid-fast bacilli that are found 

 in tissues and secretions not communicating with the outer world 

 (unopened lymph glands, deep cheesy foci, tissue of the udder) as 

 tubercle bacilli while similar findings under opposite conditions can 



