1919] DRECHSLER— ACTINOMYCES 81 



Actinomyces III and VIII, where cross-walls can only rarely be 

 distinctly perceived. 



All investigators, with the exception of Schutze, agree in 

 attributing to the peripheral wall of the filament of Actinomyces 

 an extreme thinness. Indeed, Kruse (ii) and others have urged 

 the single contoured character of the membrane as an evidence of the 

 bacterial affinity of the genus. It is only necessary to examine 

 fungus forms like Chlorosplenium or PJwma, to convince one's self 

 that the single contoured wall is generally characteristic of minute 

 cells, whatever their taxonomic connections may be. Yet while 

 the phylogenetic inference may safely be rejected, it still remains 

 true that the peripheral wall of every species of Actinomyces, except 

 possibly those of some old enlarged hyphae, cannot be made out as 

 a distinct structure with double contour. In evacuated portions 

 its location is indicated by only the faintest indication of its outline. 

 Nor is this surprising when we consider that the maximum resolv- 

 ing power of any combination of lenses employing visible light is 

 approximately 0.17 ju. As this magnitude barely equals the 

 widths of the thinnest cross-walls observed, it is not difficult to 

 suppose that, in the t)pe of sporogenous hyphae represented in 

 Actinomyces XIII, the dimensions of the partitions, like the fila- 

 ment wall generally, fall below the limit of visibility. 



It is pertinent in this connection to emphasize the peculiarity 

 in the nature of the cross- walls, the appearance of which in many 

 species of Actinomyces initiates the development of the individual 

 spores. Their unusual relative thickness, even in species in which 

 they can be distinguished only with difficulty, but where neverthe- 

 less their thickness must exceed o . 17 /x, in filaments with a diameter 

 of only o . 9 /x, is indicative of a composition essentially different 

 from that of the peripheral wall. This indication is strengthened 

 by the strong affinity for dyes characteristic of the septa, the evi- 

 dent ease with which they permit of the passage of food material, 

 and their apparent plasticity of behavior, resulting in a median 

 split in some species, and in others in a gradual constriction followed 

 by a slow transformation into an attenuated isthmus. 



The disappearance of the deep staining derivatives of the septa 

 from the ends of the young spores is in some species accompanied 



