288 ACTINOMYCOSIS AND ALLIED DISEASES. 



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

 all sizes below this may be found. When suppuration is pres- 

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

 are embedded in the granulation tissue, but are usually sur- 

 rounded 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 de- 

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

 colonies being more or less transparent, the older ones being gen- 

 erally opaque. Their colour is modified by the presence of pig- 

 ment and by degenerative change, which is usually accompanied 

 by a yellowish coloration. They are generally of soft, some- 

 times 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. The parasite, which is now gen- 

 erally regarded as belonging to the streptothrix group of the 

 higher bacteria (the actinomycetes group of Lachner-Sandoval, 

 p. 16), presents pleomorphous characters. In the colonies, as 

 they grow in the tissues, three morphological elements may be 

 described, namely, filaments, coccus-like bodies, and clubs. 



i. The filaments are comparatively thin, measuring about 

 .5 At 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 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 



