ACTINOMYCES BO VIS. 441 



quent fragmentation of the contents of the long threads, 

 and later may be outside of the empty membranes (Fig. 

 20, c). These are not endospores! Older clubs become 

 notched and cut, so that structures like an asparagus 

 head may occur (Fig. 20, a). Often branched threads 

 reach far beyond the zone with the clubs (Fig. 20, d). 

 Sometimes clubs are entirely absent. Many actinomyces 

 masses are dead when expelled in pus. 



In cultures the branching mycelium is easily obtained 

 (65, ix); the clubs are found only in the deepest layers 

 of the nutrient medium. 



Staining Properties. — The threads, but not the clubs, 

 are best stained by Gram's method; afterward the clubs 

 may be stained red with saffranin and diffusely staining 

 carmine. According to Berestnew (Z. H. xxix, 94), young 

 actinomyces clubs stain byZiehl's method, sometimes also 

 by Gram's method. 



Relation to Oxygen. — Grows aerobically and anaero- 

 bically, but better aerobically (Bostrom). The growth is 

 limited. 



Chromogenesis. — The production of pigment is ex- 

 ceedingly variable; from white to various shades of yellow, 

 orange, rusty, and brown appear to occur upon the various 

 nutrient media; the darker tones at least predominate 

 upon serum media, the brighter ones on gelatin. 



Gelatin Plate. — (a) Natural size: After six days the 

 colonies have a very irregular outline, are yellowish- 

 gray, shining, sometimes fairly elevated above the sur- 

 face of the gelatin, sometimes growing deeply into it (65, 



IV). 



(6) Magnified sixty times: Dark yellowish-gray, homo- 

 geneously shaded colonies, sometimes presenting more 

 or less distinct concentric rings. The peripheral zone is 

 dark and beset with fine, curly hair (65, vii). 



Gelatin Stab. — Surface growth at first is whitish-yellow, 

 flatly elevated, faintly shining, rather tough ; later the 

 growth sinks into the gelatin with the limited liquefaction, 

 leaving an air-space above. In the stab at first there are 

 small yellowish-white clumps, which later have bristly 

 outgrowths (65, iii). 



Agar Plate. — Macroscopically and microscopically 



