CHARACTERS OF THE ACTINOMYCES. 261 



Naked -eye Characters of the Parasite. The actino- 

 myces grows in the tissues in the form of little round masses 

 or colonies, 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. Their colour is modified by the presence of pig- 

 ment and by degenerative change, which is usually accom- 

 panied by a yellowish coloration. 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 occasion- 

 ally the case ; in fact, in the human subject they occur much 

 more frequently as small specks of semi-translucent appear- 

 ance, and of greenish-grey tint. 



Microscopical Characters. There is still dispute as to 

 the exact botanical position of the actinomyces, though 

 most authorities regard it as a pleomorphous bacterium 

 belonging to the streptothrix forms (p. 19). This view 

 appears to us to be the correct one. In the colonies, as 

 they grow in the tissues, three morphological elements may 

 be described, namely, filaments, cocci, and clubs. 



i. The filaments are comparatively thin, measuring about 

 .5 fj. 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, sometimes contains 

 granules of dark pigment. In the centre of the colony the 



