MICROSCOPICAL CHARACTERS. 



289 



constituted by filaments loosely arranged ; but later, part of the 

 growth may become so dense that its structure cannot be made 

 out. This dense part, starting excentrically, may grow round 

 the colony to form a hollow sphere, from the outer surface of 

 which filaments radiate for a short distance (Fig. 101). The 

 filaments usually stain uniformly in the younger colonies, but 

 some, especially in the older colonies, may be segmented so as 

 to give the appearance of a chain of bacilli or of cocci, though 



FlG. 101. Actinomycosis of human liver, showing a colony of the parasite composed 

 of a felted mass of filaments surrounded by pus. 



Paraffin section ; stained by Gram's method and with safranin. X 500. 



the sheath enclosing them may generally be distinguished. 

 Rod-shaped and spherical forms may also be seen lying free. 

 2. Coccus-like Bodies. The formation of these from fila- 

 ments has already been described, but it is doubtful if all are of 

 the same nature. Like other species of streptothrix, the acti- 

 nomyces when growing on a culture medium shows on its sur- 

 face filaments growing upwards in the air, the protoplasm of 

 which becomes segmented into rounded spores or gonidia. In 

 natural conditions outside the body these gonidia become free 

 and act as new centres by growing out into filaments. They 

 have somewhat higher powers of resistance than the filaments, 

 though less than the spores of most of the lower bacteria. It is 



