290 ACTINOMYCOSIS AND ALLIED DISEASES 



much older colonies, the clubs constitute the most prominent 

 feature, whilst in most colonies the filaments are more or less 

 degenerated, and it may sometimes be impossible to find any. 

 They often form a dense fringe around the colony, and when 

 stained by Gram's method retain the violet stain. They have, 

 in fact, undergone some further chemical change which produces 

 the altered staining reaction. Occasionally in very chronic 



FIG. 98. Colonies of actiuomyces, showing general structural arrangement 



and clubs at periphery. From pus in human subject. 



Stained Gram and safranin. x 60. 



lesions in the human subject the clubs stain with Gram's 

 method. Clubs showing intermediate staining reaction have 

 been described in the ox by M'Fadyean. The club-formation 

 probably represents a means of defence on the part of the 

 parasite against the phagocytes of the tissue : the view, formerly 

 held, that the clubs are organs of fructification has now been 

 generally abandoned. 



Tissue Lesions. In the human subject the parasite pro- 

 duces by its growth a chronic inflammatory change, usually 

 ending in a suppuration which slowly spreads. In some cases 



