326 APPLIED BACTERIOLOGY 



cocci become invested with a gelatinous material, and 

 multiply by division, giving rise to irregularly - shaped 

 zoogloea masses, sometimes of enormous size. When cul- 

 tivated in marsh-water the cocci grow into rods, which by 

 continuous division form filaments which radiate out in 

 all directions from the zoogloea. When this growth has 

 attained a certain age, a sheath is produced which contains 

 ferric hydrate. By a continual process of division which 

 takes place within the sheath, such a pressure is exerted 

 against its top end that it is forced open, and thus the 

 rods and cocci escape. Sometimes the cocci and rods 

 develop within the sheath into rods and threads, and push 

 their way through the walls of the sheath, giving rise to a 

 paint-brush appearance. 



(b) Beggiatoa. — The Beggiatoa are distinguished by the 

 presence of grains of sulphur in the cells, which are seen 

 as highly refracting granules. The Beggiatoa are widely 

 distributed, and are found both in fresh and salt water con- 

 taining decomposing vegetable and animal matter. In the 

 waters of sulphur springs they are especially abundant, and 

 accumulate upon the muddy bottom, or upon the organic 

 matter undergoing decomposition, as a white, gray, 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 for 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 



