SYSTEMATIC AND DESCRIPTIVE. 26 I 



irregular; their ends are cut off bluntly, and they 

 exhibit rapid movement. They occur abundantly 

 in marsh-water in summer, and can be obtained 

 by allowing algae to decompose in water (Fig. 99). 

 On cultivation the threads break up into long rods, 

 short rods, and finally cocci. This change is ren- 

 dered visible by making cover-glass preparations, 

 and staining with aniline dyes. 



FIG. 99. SPIRILLUM PLICATILE (Marsh Spirocha-te). From sewage- 

 contaminated water, X 1200. 



The following may be provisionally described as dis- 

 tinct species, though they are probably the spiral phase- 

 forms of protean species. 



Spirillum serpens, Miiller (Vibrio serpens). 

 Threads 11 28 //, long, '8 ri //, thick, with three or four 

 windings. They are actively motile, often united into 

 chains, or forming swarms, and are abundant in stagnant 

 liquids. 



Spirillum tenue. Very thin threads, with at least 

 ij, usually 2 5 spirals. Height of a single screw is 

 2 3 //,, and the length of spiral, therefore, 4 15 /u.. They 

 are very swiftly motile, and often occur in felted dense 

 swarms in vegetable infusions. 



Spirillum undula. Threads i- 11-4 /* thick, 9 

 12 fjL long; spirals 4-5 /x, high; each thread has if 3 

 spirals. They are actively motile, and possess at each end 

 a flagellum. They occur in various infusions (Fig. 100). 



Spirillum volutans, Ehrenberg. Threads 1-5 



