244 3iauual of Veterinary Mierohiotogy . 



meet with an organism endowed with great recep- 

 tivity; in such case these protective elements have 

 not time to become developed and the tubercle is al- 

 most entirely lymphoid. 



The extension of the inflammatory pjrocess to the 

 capillaries involves their obliteration and the absence 

 of the reparative plasma in the central parts of the 

 tubercle. Thus is explained the necrobiosis (coagu- 

 lative necrosis) so frequent in this lesion, although 

 the influence of the secretions of the bacillus upon 

 the organic elements must also be taken into account 

 in this connection. This toxic action of the bacillus 

 is the more pronounced in inverse proportion to" the 

 resisting power of the organism ; thus, in spermo- 

 philes the giant cells of which destroy many bacilli and 

 establish their superiority over them, caseous masses 

 are not found even after a tuberculosis of long dura- 

 tion. 



Tubercular lesions are usually localized at the point 

 of entry of the germs; the disease is, therefore, pri- 

 marily local, and it may definitely remain in this con- 

 dition. More frequently, however, it extends, and 

 this extension takes place in diflerent ways. In man 

 and the large animals extension occurs chiefly by the 

 lymphatics, but it may also occur by way of the blood 

 circulation when the bacilli have penetrated into the 

 blood through ulceration of a vein at a diseased fo- 

 cus, or, indeed, through the medium of the lymphatic 

 vessels. 



We have already seen that the first mode of propa- 

 gation predominates in the guinea pig, whilst it is 

 only accessory in the rabbit. 



Virulent products coming from one part of the or- 



