ALG^ 251 



pinkish or violet layer; the bottoms of ponds, springs, etc., 

 are often coloured reddish by the abundant growth of this 

 organism. 



Mayer has shown that they are able to decompose sul- 

 phate of soda in organic solutions suitable i^ their growth. 

 Like the previously described genus (Crenothrix), spherical, 

 rod-like, filamentous and spiral forms are included in the 

 life-history of the species. The filaments show a differentia- 

 tion as to base and free-growing extremity ; but, unlike 

 the crenothrix, the segments into which the filaments divide 

 are not included in an external sheath. The filaments are 

 flexible, and exhibit a gliding movement ; they are able to 

 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 huccalis, 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 manufac- 

 tories. In Eussia it frequently occurs in the water-supplies 

 of towns. It is to be obtained from the surface of putrefy- 

 ing vegetables or animal matter immersed in river or 

 swamp water. 



