ALG^ 



327 



multiply abundantly in hot sulphur waters having a tem- 

 perature of 55° C. and above. 



(c) Leptothrix.— These are distinguished from Beggiatoa 

 by the absence of sulphur grains, and from the Crenothrix 

 by the fact that the segments are not enveloped in an 

 exterior sheath, as well as by the comparative thinness of 

 the cylindrical segments, otherwise they present the same 

 variety of forms as has been ascribed to the Beggiatoa and 

 Crenothrix, All the varieties of Leptothrix are common in 

 the mouth and slime of the teeth. One of them, the 

 Leptothrix buccalis, is believed to be intimately connected 

 with dental caries. The threads penetrate the tissue of the 

 teeth, after the enamel has been acted upon by the acids 

 generated by the fermentation of the food. 



Cladothrix Dichotoma.— This is the commonest micro- 

 organism occurring in both stagnant and running water in 

 which organic matter is present. It is frequently found in 

 the refuse- water of factories, especially sugar manufactories. 

 In Eussia it frequently occurs in the water-supplies of 

 towns. It is to be obtained from the surface of putrefying 

 vegetables or animal matter immersed in. river or swamp 

 water. 



It consists of long, motionless filaments which sometimes 

 grow to a millimetre in length, and which may possess 

 pseudo-branches. According to Zopf, the cocci-like repro- 

 ductive elements grow into rods, and these into fine 

 filaments, from which latter the pseudo-branches are given 

 off. This apparent branching of the filaments is the dis- 

 tinguishing generic character of the species. The sheaths 

 of the filaments are often coloured yellow, red, olive-green 

 or brown by oxide of iron. The Cladothrix dichotoma with- 

 draws iron from water, and thus fixes it, often causing 

 obstructions in iron pipes. 



Cladothrix dichotoma can be readily cultivated on in- 



