1 9 1 9] DRECHSLER—ACTINOM YCES 



155 



crust of old mature spores; tyrosinase reaction absent; substratum 

 stained a faint greenish yellow in old cultures. 



Morphology.— According to Waksman and Curtis, the aerial 

 filaments of this species possess only a sHght tendency to branch. 

 The writer was led to a somewhat dififerent conclusion, as the axial 

 hyphae are usually found to proliferate fertile branches at mod- 

 erately close intervals. Occasionally, as jn fig. 58, indications of 

 a successive sequence may be observed, but more frequently the 

 de\'elopment of the different elements of a ramifying system occurs 

 without any recognizable interrelation. The short, cylindrical 

 spores, 0.7X0.7-1 .0 ;u, are formed, as in Actinomyces XVI, by 

 a septation of the fertile h\phae, followed by sphtting of the parti- 

 tions along a median plane, but the septa are usually less conspicu- 

 ous, and often not clearly visible, and the fertile hyphae show no 

 indication of a spiral condition. 



A striking dimorphism characterizes the mycelium of this 



species, as well as that of a number of other forms observed by the 



writer. The deeper sterile aerial h>phae below the sporogenous 



layer tj^Dically are extremely minute, with a diameter frequently 



not exceeding o .3 /x; their protoplasmic contents show Httle affinity 



for stains; and the contours of their walls are uniformly smooth. 



The more superficial hyphae, which usually attain a thickness of 



i.o/x, and are distinguishable by markedly irregular contours, 



contain dense deep staining protoplasm; and when septa are 



present, they are sometimes associated, as in Actinomyces XVII 



and XVIII, with spherical structures. The thicker filaments bear 



the sporogenous branches, and, in general, appear to constitute the 



expanded prolongations of the minute hyphae (fig. 59). 



Isolated twice from soil collected in Cambridge, Massachusetts; once from 

 tap water; very frequently from outdoor air; several times from gross cultures 

 of dead leaves; 4 times from horse dung undergoing fermentation at 50-60° C. 



Synonomy. — In his description of Streptothrix alba, Rossi- 

 DoRiA records two characteristics that estabhsh its identity 

 beyond much danger of confusion: a conspicuous preponderance 

 in number over any of its congeners on plates exposed to the 

 air, and a tendency toward the formation of concentric rings 

 more pronounced than that of any other species. Rossi-Doria 



