8o Lectures on Bacteria. [$ vm. 



are known in the green Oscillatorieae, which have been noticed 

 already several times, and which are undoubtedly the near allies 

 containing chlorophyll of the species of Beggiatoa and of the 

 arthrosporous Bacteria. The movements consist in progression 

 in the line of the axis of the filament in one direction, or in 

 opposite directions alternately, together with rotation in a path 

 which forms the outline of a very pointed cone, or of a 

 double cone such as is described in the case of rod-shaped 

 Bacteria. These movements, when hastily observed, appear 

 to be gliding in a forward direction, while the ends of 

 the filaments swing hither and thither in the manner of a 

 pendulum. Sometimes also the filaments become curved, and 

 then often straighten themselves again with a jerk, showing their 

 great flexibility throughout their entire length. 



Several other species of Beggiatoa are known : B. roseo-per- 

 sicina, distinguished by its rose-red to violet colour, and also 

 said to be pleomorphous, its Zoogloeae, according to Zopf, 

 being Cohn's Clathrocystis roseo-persicina ; B. mirabilis, Cohn, 

 known only in the filamentous form, a gigantic species 20-30 /A 

 in thickness; B. arachnoidea, Roth, and some others. Apart 

 from the differences indicated, all these agree with B. alba in the 

 characteristic marks, especially in the presence of sulphur-grains. 



B. alba is one of the most common inhabitants of our waters. 

 It is found in the water of marshes, in the waters that flow 

 from manufactories, in hot sulphur-springs, and in these places 

 often in company with Cladothrix, and in the sea on shallow 

 coasts. B. roseo-persicina is less common in these localities ; 

 the other species mentioned above are known only as coming 

 from the sea. The species of Beggiatoa live on the decompos- 

 ing remains of organised bodies, especially plants; they are, 

 therefore, chiefly found at the bottom of water, where such objects 

 accumulate. They form there, when largely developed, slimy 

 membranous coverings or films of flocculent matter, which are 

 either white in colour or vary from rose to brown-violet, as in 

 B. roseo-persicina. 



