312 



THE MICROSCOPE AND ITS REVELATIONS. 



ture. They present themselves abundantly in infusions of decomposing 

 organic matter, in combination with other Bacteria forms, from which 

 they are distinguishable by their wavy serpentine movement. The 

 length of one of the commonest species, V. rugula (Fig. 196), is usually 

 from l-l,200th to l-2,500th of an inch. 



Four individuals of Vibrio rugula, each showing flagellum at one or both ends; two other 

 individuals, a and b, separating from each other, and drawing out protoplasmic filament to their 

 flagella. Magnified 2,000 diameter. 



308. Spirilla, which are the largest of the whole group, are charac- 

 terized by the spiral coiling of their cells (Fig. 197), and by their cork- 

 screw-like movement; and are found not so much in newly decomposing 

 infusions of organic matter, as in stale liquids which have passed through 

 the active stages of putrescence. Nothing has been certainly known, 

 until recently, of their life-history; but the observations of Messrs. 

 Geddes and Ewart ' seem to render it clear that they pass through a, 



A, Spirillum undula, showing flagellum at each end. Magnified 3,000 diameters. B, Spirillunt- 

 volutans. Magnified 2,000 diameters. 



series of stages closely corresponding to those of Bacillus. The ' zooglaea ' 

 film formed by the aggregation of /Spirilla has a brownish tint; some of 

 the organisms of which it is composed are at rest, and others in rapid 

 movement. The resting Spirilla are sometimes nearly straight, with a 

 slight curvature at one or both ends, the curve increasing until the 

 characteristic spiral of the motile form is attained; and the change from 

 the still to the motile state may take place very rapidly, often with a 

 passage through a transition Vibrio stage. But Spirillum, like the 

 forms already described, may lengthen out into long filaments, which 

 lose their characteristic twist and their motile powers; and their endo- 

 plasm breaks up into spores, which, after their escape from the filaments, 

 form a distinct capsular investment, which holds them together in groups 

 while multiplying by subdivision. Sometimes, again, a mere cellulose 



1 " Proceedings of Royal Society," June 20th, 1878. 



