158 



OUTLINES OF BACTERIOLOGY 



FIG. 100. Gallionella ferru- 

 ginea. 



lately that it has been accurately studied. Each individual consists of 

 a long fine thread, which winds in such a manner that it looks like 

 a hairpin closely and spirally twisted round itself. All sizes can be 

 seen in a favourable culture, from very small ones (Fig. 100J) to much 

 larger examples (Fig. lOOa). It usually occurs 

 in very small numbers along with Leptothrix 

 ochracea, the latter usually greatly prepon- 

 derating; very rarely it forms the chief 

 organism in iron-water. The thread is not 

 divided in any way, and the ends are rounded 

 off like those of bacilli. According to Migula 

 a very delicate external membrane is present, 

 though later observers have failed to find it. 

 The average diameter of a thread is about 1 /i, 

 but may be as small as J ^ and as large as 1*5 fj.. 

 The loops formed by the twisting vary con- 

 siderably both as to size and number. There 

 may exceptionally be as many as 35 belonging 

 to one thread. 



The method of multiplication is of two 

 kinds. The commoner of the two is by divi- 

 sion. Small portions are cut off, which immediately curl up, and by 

 growth produce the normal thread (Fig. 100/>). The other method is 

 by the formation of conidia, which arise in exactly the same manner 

 as in Leptothrix ochracea. Examples of conidia 

 formation are shown in Fig. 101. It is interesting 

 to note that preparatory to conidia formation the 

 coils somewhat loosen themselves, so as to allow 

 a greater surface to come into play for this purpose. 

 The conidia are slightly oval, about 1 //, in breadth 

 and 1-5-1-75/A in length. The stages of germina- 

 tion have not yet been observed. 



Clonothrix fusca (Schorler). In 1904, another 

 member of this group was found in the water- 

 works in and about Dresden. It combines the 

 characters of Crenothrix and Cladothrix in that while 

 the individual threads are like Crenothrix polyspora in shape and in 

 their methods of reproduction, they are like Cladothrix dichotoma in 

 forming false branches. The threads are unequally thick, the bottom 

 part measuring 5-7 ^ in thickness, whilst the upper part may be any- 

 thing up to 2 fj.. The cells in the thread are normally 6-8 ft long, but 



Fio. 101. Gallionella 

 ferruginea. Showing 

 conidiu rn -formation . 



