76 Lectures on Bacteria. [ vm. 



of their own. These minute cells may be called Cocci from their 

 form, or spores on account of their capability of further de- 

 velopment, for when cultivated in bog-water they develope into 

 new filaments resembling the parent-filaments (d, e). ' On the 

 other hand they may retain the Coccus-form and multiply, pro- 

 ducing at the same time a large quantity of jelly, and in this 

 state they form Zoogloeae, which vary in size from microscopical 

 minuteness to more than i cm. in diameter. They also occa- 

 sionally pass, according to Zopf, into the motile condition, and 

 back again into the resting-state. The Zoogloeae are at first 

 without colour, but like the sheaths of the filaments they gradu- 

 ally become coloured by deposition of iron. The Cocci also 

 may ultimately develope from the Zoogloea-state into the fila- 

 ments as at first described. The external conditions for these 

 formations are not certainly understood. 



Crenothrix Kiihniana is found in every kind of water, even in 

 the water of the soil as far as twenty metres below the surface. 

 It may become a formidable nuisance in water-pipes, drain- 

 pipes, and the like, in which its tufts of filaments and its Zoo- 

 gloeae increase to such an extent as to form dense gelatinous 

 masses stopping up the passages; in reservoirs it may form 

 slimy layers several feet in depth. The water is thus ren- 

 dered unfit for drinking and for various technical uses, though 

 no direct injury to human health has been traced to the Creno- 

 thrix. We do not know that any other processes of decom- 

 position are caused by Crenothrix. 



2. Cladothrix dichotoma, Cohn is of still more frequent occur- 

 rence than Crenothrix, especially in dirty water, such as the 

 outflow from manufactories and from similar sources, and also 

 in streams (Fig. 6). It often forms extensive films of flocculent 

 matter of a grayish white colour floating near the edge of the 

 water. Its delicate filaments, ensheathed as in the preceding 

 species, are chiefly distinguished from those of Crenothrix in 

 the full-grown state by being branched. Branching is effected 

 by any single cell of a filament bending one of its extremities 



