INFECTIOtJS DISEASES. 



second or two, but when the epithelium has been shed as a conse- 

 quence of laryngitis or pharyngitis, infection may occur. 



As regards cutaneous inoculation, the parasite only seems dan- 

 gerous when the skin is excoriated or injured either accidentally or 

 as the result of surgical interference. 



Actinomycosis of the lung is probably caused by the germs being 



inhaled along with 

 the inspired air. 



Lesions. The 

 lesions are very pe- 

 culiar in character, 

 and end in com- 

 pletely destroying 

 the tissues invaded. 

 Once lodged 

 within an organ, 

 the disease shows 

 a tendency to ex- 

 tend in all direc- 

 tions, and, despite 

 the defensive reac- 

 tion of the tissues, 

 it soon forms 

 numerous parasitic 

 centres. 



In bones, for 

 example, actinomy- 

 cosis invades the 

 spongy tissue with 

 the greatest ease. 

 It causes subacute 

 ostitis, which leads 

 to diffuse suppura- 

 tion and local 

 hypertrophy of the bone, destruction of the compact layers, and the 

 development of an abscess with fungoid, exuberant, granulating walls 

 which show no reparative tendency whatever. 



The pus of the abscess and the liquid from the fistula contain 

 varying quantities of yellowish grains, representing clusters of actino- 

 myces. The surrounding tissues, muscles, tendons, skin, etc., are all 

 involved before long in the inflammatory process, and the granulating 

 masses themselves are invaded by the yellowish parasitic tufts. All 

 the fistulse are surrounded by enormous zones of infiltration, which on 



Fig. 274.- 



-Old-standing bone lesions in a case of 

 actinomycosis of the jaw. 



