BACTERIA. 



37 



N 



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\< 



S 



sporous; the spore-forming cells swell, assume very different forms, 

 and show granulose reaction. The germ-tube grows out in the 

 direction of the long axis of the spore. 



Bacillus snbtilis, the Hay-bacillus, is developed in all decoctions 

 of hay ; a slender, aerobic, self-motile Bacillus ; endosporous (aplano- 

 spores) ; the spore-wall ruptures transversely on germination. 



Crenothrix kilhuiana occurs in the springs of many baths, in 

 wells, in water or drain-pipes. 



Beggiatoa (parallel with the Blue-green Alga Oscillaria). Long 

 filaments formed of cylindrical cells which are attached by one of 

 the ends, but which are nearly always free when observed. The 

 filaments, like those of Oscillaria, describe conical figures in their 

 revolutions, the free filaments slide upwards and parallel with one 

 another; sheaths are wanting ; strongly 



refractive sulphur drops are found in the *| ^ r\ 



interior. The Beggiatoas are the most W H y\ 



iriai IE a 



prevalent Sulphur-bacteria. They occur, 

 very commonly in large numbers, wher- 

 ever plant or animal remains are de- 

 caying in water in which sulphuretted 

 hydrogen is being formed ; thus, for ex- 

 ample, B. alba (Fig. 31) occurs frequently 

 as a white covering or slimy film on mud 

 containing organic remains. B. mirabilis is 

 remarkable for its size and its strong peristaltic 

 movements. The Sulphur-bacteria oxidize 

 the sulphuretted hydi-ogen, and accu- 

 mulate sulphur in the shape of small 

 granules of soft amorphic sulphur, which 

 in the living cell never passes over into 

 the crystalline state. They next oxidize 

 this sulphur into sulphuric acid, which 

 is immediately rendered neutral by ab- 

 sorbed salts of calcium, and is given 

 off in the form of a sulphate, thus CaC0 3 is principally changed 

 into Ca SO 4 . In the absence of sulphur the nutritive processes 

 are suspended, and consequently death occurs either sooner or 

 later. The Sulphur- bacteria may exist and multiply in a fluid 

 which only contains traces of organic matter, in which organisms 

 devoid of chlorophyll are not able to exist. The Beggiatoas 

 very frequently form white, bulky masses in sulphur wells and 



y 



8 



FIG. 31. Beggiatoa alba: a 

 from a fluid containing abund- 

 ance of sulphuretted hydrogen ; 

 I) after lying 24 hours in a solu- 

 tion devoid of sulphuretted 

 hydrogen ; c after lying an 

 additional -48 hours in a solution 

 devoid of sulphuretted hydro- 

 gen, by this means the trans- 

 verse walls and vacuoles have 

 become visible. 



