528 SPIRILLUM 



varies from about 0-3 to 1-0//, and the amplitude of the spirals from about 0-8 to 

 2-0 [JL. Even amongst different organisms of the same strain, there is often con- 

 siderable variation in the number and size of the spirals ; together with organisms 

 showing regularly disposed spirals, there may be seen others of two or three times 

 the length, with only one or two irregular undulations. In shape the whole organism 

 may be straight, or it may be bent in one or more places, generally acutely. Fila- 

 mentous forms are not uncommon. On agar or gelatin the spiral shape may be 

 almost lost, and the organisms closely resemble vibrios. As a rule the curvature 

 is very marked, and there is a tendency for the organisms to be arranged in pairs 

 end-to-end with the concavities facing in the same direction, so as to present a 

 scalloped appearance ; s-shaped forms too are common. In young cultures the 

 spirilla are motile — generally by tufts of flagella at the poles. Unlike the spiro- 

 chaetes, the spirilla stain readily with the ordinary aniline dyes, and are usually 

 Gram-positive. Growth is fairly free, though not abundant, on the ordinary 

 media. Most of the water spirilla form a pigment of red, yellow, or greenish- 

 yellow colour. The pigment, at least of Sf. ruhrum, is formed most readily at a 

 low oxygen pressure ; it is well marked in the depths of gelatin stab cultures, and 

 hardly noticeable on surface growths. The optimum temperature for growth is 

 25-30° C. as a rule. Aerobic conditions are preferred ; growth under strict 

 anaerobiosis is very slight. None of the species forms spores, and none is par- 

 ticularly resistant to heat or disinfectants. The biochemical characteristics have 

 not been fully studied. None of the members except »S'^jm7/Mm minus (seep. 1838) 

 is pathogenic for man or animals. We append a description, based largely on 

 personal observations, of Spirillum ruhrum. 



Spirillum rubrum 



Isolation. — Esmarch 1887, from a mouse decomposing under water. 



Habitat. — Water. 



Morphology. — On solid media the organisms are sharply curved rods, 2—3 /i X 0-4 ,m, 

 arranged singly and in s-shaped or semicircular pairs. In fluid media long spirals 

 are formed, 3-10 ^ or more in length. The axis of the spiral is straight, or bent 

 sharply at a right-angle ; the number of spirals varies from about 1 to 8. Ends 

 are sharp, drawn out, or sometimes blunt. Long thread-like forms also seen. 

 Motile by bundles of flagella at both poles. Gram-positive. 



Agar Plate. — 2 days at 28° C. Round, 0-4 mm. in diameter, convex, amorphous, 

 almost colourless and transparent colonies with smooth glistening surface and 

 entire edge ; consistency butjTOus ; easily emulsifiable. 7 days ; rather larger 

 and of a pinkish colour. 



Agar Stroke. — 2 days at 28° C. Poor, slightly raised, and almost transparent, partly 

 confluent growth, with irregular surface, and edge formed of single colonies. 7 

 days ; slight pinkish coloration. 



Gelatin Plate. — 4 days at 23° C. Small, 0-3 mm. in diameter, water-clear, convex 

 colonies, with smooth surface and entire edge. No liquefaction. Deep colonies 

 are pink. 



Gelatin Stab. — 5 days at 23° C. Poor to moderate, filiform growth of very tiny discrete 

 red colonies, extending nearly to bottom of tube. No surface growth ; no lique- 

 faction. 



Broth. — 2 days at 28° C. Moderate growth with slight turbidity, and a pale pink flocculo- 

 granular deposit, not disintegrating completely on shaking ; no surface growth. 



MacConkey.—l days at 28° C. No growth. 



