1919] DRECHSLER— ACTINOMYCES 75 



generally follows. This increase may be slight, as in some species 

 in which the mature sporogenous hyphae are still somewhat 

 thinner than the vegetative hyphae (fig. 46), or more considerable, 

 as in forms in which they conspicuously exceed the latter in thick- 

 ness (figs. 4-6). The very simple type represented by Actinomyces 

 XIII, in which the aerial mycelium is represented by very long 

 filaments, rarely branching and apparently sporogenous almost to 

 their point of origin in the nutritive mycelium, constitutes the only 

 exception, since in this instance there is no indication of thickening 

 in the young fertile hyphae, nor indeed any variation in the diameter 

 of its vegetative filaments. 



In a majority of the species the maturation of the sporogenous 

 h>phae is associated with a peculiarity in growth by which they 

 become coiled in more or less characteristic spirals. The tendency 

 toward the coiled condition is usually clearly manifested before the 

 branch has grown to half its final length through the open flexuous 

 habit of the young filament (figs. 5^2, 107). As elongation con- 

 tinues, the turns become increasingly definite, but the contraction 

 leading to the fijial condition, which ranges from that illustrated 

 by Actinomyces XIII with its open, barely perceptible turns, to one 

 in which the spirals are so strongly compressed that its adjacent 

 turns are in continuous contact (figs. 44, 51, 57) in a fashion resem- 

 bling that of the spores of the h>'phomycetous genus Helicobn, is 

 usually delayed until the later growth in thickness of the filament. 

 Specific differences may not only be indicated by the obliquity of 

 the spiral, but involve also the number and diameter of its turns, 

 and its construction with reference to the dextrorse or sinistrorse 

 condition. The range in different species extends from the 2 or 3 

 turns exhibited in forms like Actinomyces II and XVI, to over 

 20 turns in others; but the range in a particular species is always 

 considerably smaller. The writer once observed a spiral with 24 

 turns, but this probably approximates the extreme maximum; 

 spirals with 14-16 turns (figs. 23, 57, 94c) are by no means abundant, 

 and probably no species produces many in which there are more 

 than 12 turns. 



The diameter of the spirals as a whole is more or less in inverse 

 ratio to the number of turns characteristic of the species. This 



