STRUCTURAL CHANGES DUE TO DAMAGE. 



321 



vessels and carry the infection to all parts of the body, occasioning 

 general tuberculosis. 



The poisonous products of the tubercle bacilli are absorbed into 

 the general system, producing disturbances of nutrition, emaciation, 

 and fever. Old encapsulated tubercular products are prone to 

 calcareous infiltration, but, even after prolonged encapsulation, 



FIG. 284. 



-'^s" /'*' *" . * '> ^ "/* * 

 . <? ,*^*'-' * . 



ililiary tubercle ; lung of a horse. (Birch-Hirschfeld and Johne.) Cheesy degeneration has 

 only just begun in the centre of the focus of inflammation, where the nuclei of epithe- 

 lioid cells and leucocytes are still visible. At the periphery of the tubercle is a zone of 

 round-cell or leucocytic infiltration. Three giant-cells, with peripheral nuclei, occupy 

 intermediate positions; around the tubercle are the infiltrated walls of pulmonary 

 alveoli. 



the tubercle bacilli which have been imprisoned may retain their 

 vitality, and, if for any reason the poorly nourished capsule suffers 

 in its integrity, these old nodules may become the source of fresh 

 infection. This is a not uncommon result of some acute disease like 

 scarlet fever, typhoid fever, or influenza, convalescence from those 

 diseases being followed by the development of tuberculosis spring- 

 ing from an old and long-dormant tubercular infection. 



In the lungs the tubercles, as they increase in size, involve the 

 walls of the alveoli or the bronchi, and when the cheesy matter 

 21 



