TUBERCULOSIS 275 



foretell wlien the closed form of the disease will change to 

 the open, as it is certain to do if the disease progresses. 

 Hence every affected animal must be considered a potential 

 source of danger to the herd and to public health. 



The tubercles vary in size from a pinhead to abscesses as 



Fi;:. 44. A TiilM-rnilar Sploon 



This oixun shows a number <>f tuh.'ivlcs. It is ;m rsainplo of tuberculosis in 

 dm 1 to the feeding of infected milk 



large as the closed fist. The small tubercles are usually of 

 a light pearly gray color throughout, or they may show a 

 yellowish area at the center, composed of dead tissue. The 

 larger tubercles and abscesses may be filled with creamy 

 pus, or with hard, gritty yellow material due to the depo- 

 sition of lime salts. The tubercle is then said to be calci- 

 fied, and its contents have the appearance of corn meal. 



The lungs of a healthy animal are light pink in color and 

 spongy in texture; in the tubercular organ the firm, hard 

 tubercles may be felt upon pressure, or they may even be 

 raised above the surface of the lung. As has been stated, 

 the disease is readily recognized in the liver and spleen 

 by the sharp contrast between the yellow affected areas and 

 the surrounding healthy tissue. 



Tubercular organs and glands are usually increased in 

 size in comparison with the healthy tissue. In the case of 

 a tubercular udder the disease is usually confined to a single 

 quarter and the affected part may be much enlarged. 



