Pathogenesis. 649 



tlie iidcler tlirongli the milk ducts thus causing the comparative 

 frequency of affection of this organ in swine. 



Of the domestic animals cattle are most susceptible to 

 infection. The disease occurs much less frequently in swine 

 and only rarely in horses, sheep, goats and dogs (according 

 to Schouten it is quite prevalent among the goats in the Nether- 

 lands). Breed or sex have no influence on the development of 

 the disease, although the seat of the morbid process is de- 

 termined by the age of the animal. Thus in young cattle 

 actinomycosis of the pharyngeal region is quite common while 

 actinomycosis of the tongue is usually observed in mature 

 cattle only. 



Pathogenesis. As a result of the inflammatory reaction, 

 nodules composed of small round cells form around the para- 

 site. Some of the mycelia penetrate the tissue cells which 

 become enlarged and develop into epithelioid cells which, in 

 their turn, by division of their nuclei, develop into giant cells. 

 The cells in the interior of the nodule, wliicli resembles a 

 tubercle, degenerate and thus the center of these nodules are 

 composed of cell detritus, nucleated and free fat globules. 

 These primary nodules are surrounded by granulation tissue 

 on the periphery of which new nodules develop which are again 

 enclosed by newly formed connective tissue. In this manner 

 large spherical and lobulated tumors so called actinomycomata 

 (Johne) are developed. These may resemble in structure either 

 a soft sarcoma or have the appearance of a dense fibroma. 

 Accordingly a section of the tumor may appear homogeneous, 

 grayish-Avhite, marrow-like, or fibrinous and reddish-gray. In 

 this ground substance there may be found pale gray or yellow 

 foci of loose consistency in which are imbedded grayis]. or 

 sulphur colored actinomyces imbedded in a mucous or purulent 

 substance and having the appearance of grains of sand. These 

 foci may become confluent and thus give rise to fistulous canals 

 filled Avitli granulation tissue of a gelatinous consistency and 

 penetrating the substance of the tumor 



Actinomyces which have gained access through the mucous 

 membrane of the tongue become disseminated by means of 

 the lymph channels and give rise to the development of small 

 nodules surrounded by an area interstitial inflammation. These 

 nodules gradually increase in size, finally breaking abruptly 

 through the mucous membrane from wliicli they project like 

 a mushroom or cauliflower. In the so called groove of the 

 tongue, on the other hand, simultaneous infection with pyogenic 

 bacteria may give rise to deep ulcers. 



When these tumors develop in the interior of flat bones 

 the granulation tissue causes destruction of the bone lamellae. 

 At the same time the production of new bone tissue proceeds 

 from the periosteum, while on the other hand the development 



