CHARACTERS OF THE ACTINOMYCES 321 



which, when fully developed, are easily visible to the naked eye, 

 the largest being about the size of a small pin's head, whilst all 

 sizes below this may be found. When suppuration is present, 

 they lie free in the pus ; when there is no suppuration, they are 

 embedded in the granulation tissue, but are usually surrounded 

 by a zone of softer tissue. They may be transparent or jelly- 

 like, or they may be opaque and of various colours — white, 

 yellow, greenish, or almost black. The appearance depends 

 upon their age and also upon their structure, the younger colonies 

 being more or less transparent, the older ones being generally 

 opaque. They are generally of soft, sometimes tallow-like, 

 consistence, though sometimes in the ox they are gritty, owing 

 to the presence of calcareous deposit. They may be readily 

 found in the pus by spreading it out in a thin layer on a glass 

 slide and holding it up to the light. They are sometimes 

 described .as being always of a distinctly yellow colour, but this 

 is only occasionally the case ; in fact, in the human subject they 

 occur much more frequently as small specks of semi-translucent 

 appearance, and of greenish-grey tint. 



Microscopical Characters. — In the colonies, as they grow in 

 the tissues, three morphological elements 'may be described, 

 namely, filaments, spores' or gonidia, and clubs. 



1. The filaments are comparatively thin, measuring about 

 •6 ix. in diameter, but they are often of great length. They are 

 composed of a central protoplasm enclosed by a sheath. The 

 latter, which is most easily made out in the older filaments with 

 granular protoplasm, occasionally contains granules of dark 

 pigment. In the centre of the colony the filaments interlace 

 with one another, and form an irregular network which may be 

 loose or dense ; at the periphery they are often arranged in 

 a somewhat radiating manner, and run outwards in a wavy or 

 even spiral course. They also show true branching, a character 

 which at once distinguishes them from the ordinary bacteria. 

 Between the filaments there is a finely granular or homogeneous 

 ground substance. Most of the colonies at an early stage are 

 chiefly 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. 90). 

 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 

 the sheath enclosing them may generally be distinguished. Rod- 



