-1:64 Transactions of the Society. 



but it is not clear whether they have been expelled en bloc from 

 a sheath or if they constitute a new organism which has not yet 

 produced a visible sheath. 



In size the cells are from • 4-0 • 6 /a by • 6-6 • 5 jjl, according 

 to species. In some apparently old cells are unstained globules, 

 possibly spores. Division is by transverse fission. 



Multiplication is effected by growth from expelled vegetative 

 cells, or from sporogenous cells. 



Owing to constant growth and the hardening of the sheath, 

 cells may be expelled at the free end. False dichotomy takes 

 place only if the sheath be soft. Sometimes parallel rows of cells 

 are found in parts. For good development Sphderotilus requires 

 oxygen and nitrogenous material found in sewage. Hence its 

 presence is an indication of pollution by sewage, raw or partially 

 treated. 



The observations were carried out on specimens of natural 

 growth, by means of an artificial stream-bed, polluted by raw 

 •diluted sewage. For this purpose a porcelain drain-trough about 

 one metre long and 15 cm. wide, of right angle V section was 

 used. The trough is tilted 1-30° and a layer of marble chips 

 spread along the bottom. A thin stream of water is allowed to 

 trickle in at the top, while raw sewage drips in about 5 cm. farther 

 down. This artificial stream is inoculated with the growth. 



A single species may be obtained by plating on G.P.B., and 

 then inoculated in the artificial stream : for this small wooden 

 troughs are most suitable. 



Satisfactory growth is obtained by sterilizing with ultra-violet 

 light, sewage in Fernbach flasks in layers not more than 5 mm. 

 deep. This last method gave the best results. 



Summary. 



Occurrence. — The S'plicT.rotilus is found in streams polluted by 

 raw or partially purified sewage. It may be floating down stream 

 •or anchored to twigs, etc., immersed in stream at level water. The 

 growth is essentially aerobic. 



Size. — A sheath bacterium, sheath 2 "0-2 '8 fx broad, cells 

 • 4-0 • 6 yu- broad, and * 6-6 • 5 fju long. 



Characteristics. — False dichotomy and multiplication of threads 

 in sheath due to growth pressure. 



Optimum Temperature. — 20-25° C. 



Culture Media. — Best results have been obtained on sewage 

 sterilized by ultra-violet light. 



Preparations. — Stains well with the usual dyes ; gentian- violet 

 is perhaps the best. Slieath stains lightly, cells dark. 



