676 



INFECTIOUS DISEASES. 



this region are due to specific inoculation of external injuries. Fistulse 

 originating in the parotid region and in the upper part of the neck 

 usually resemble in appearance the maxillary fistulse. The external 

 fungoid growth, however, is less exuberant, suppuration is less abun- 

 dant, and the surrounding induration less extensive. 



Yarious localisations. Although the disease generally attacks the 

 mouth, tongue or pharynx, it may invade the oesophagus, rumen, 



Fig. 272. — Actinomycosis of mammary gland (cow). 



reticulum, liver and intestine, larynx, trachea, lung, peritoneum, 

 epiploon, and even the udder. 



Localisations in the udder and peritoneum are commonest in pigs, 

 and it is believed that inoculation occurs either through the galacto- 

 phorous sinuses or through the abdominal wounds made for purposes 

 of castration. 



Causation. The cause of actinomycosis is to be sought in the 

 development of Actiiionii/crs horis within living tissues. It seems pro- 

 blematical whether the germs to be found in the pus or saliva of 

 affected animals ever directly infect new hosts, and it is difficult to 

 carry out infection in this manner even in very sensitive experimental 



