14 . APPLIED BACTERIOLOGY 



filaments, growing out from a thinner base to a broader 



The three most important classes are : (1) Beggiatoa ; 

 (2) Crenothrix ; (3) Leptothrix. 



(1) Beggiatoa. — These form long motile threads, consist- 

 ing of colourless cells, and are distinguished by the presence 

 of strongly refracting granules of sulphur. They occur in 

 sulphur springs and in dirty water. 



(2) Crenothrix. — These form simple threads, the separate 

 cells of which surround themselves with a distinct sheath, 

 and then change themselves by segmentation at their ends 

 into roundish spores. The threads are motionless, and, 

 especially in their younger stages, group themselves into 

 little patches. 



(3) Leptothrix. — Threads with or without sheaths. 

 Division not very numerous or well marked. The cells are 

 devoid of sulphur. 



Cladotrichese. — Forms consisting of threads which pos- 

 sess pseudo-branches ; the separate cells are provided with 

 sheaths. Spore formation not yet demonstrated. This 

 class has only one division, namely Cladothrix. They are 

 found in dirty water. 



Growth of the Bacteria. — The bacteria, like the higher 

 organisms, cannot live and multiply unless they have 

 proper nourishment and conditions of growth. As the 

 bacteria do not contain chlorophyll, they are not able to 

 avail themselves of the carbon existing in the air as carbon 

 dioxide (carbonic acid gas), but are dependent for their 

 nourishment upon the more complex compounds of carbon, 

 the sugars, for instance, and the nitrogenous compounds in 

 the shape of the albuminoids. Some of the bacteria, how- 

 ever, obtain their nitrogen from inorganic materials, such 

 as compounds of ammonia and nitrates. 



The bacteria derive their oxygen either from the air or 



