The Higher Bacteria {Spherotilus). By E. M. Mum ford. 463 



exhibiting false dichotomy it does not require an iron content in 

 the stream it inhabits. 



The author is of the opinion that the group Sphserotilus com- 

 prises a number of species of higher bacteria. The type-organism is 

 characterized as a sheathed string of bacterial cells. There are two 

 sub-groups — (1) coloured and (2) uncoloured. Group 1 includes 

 S. roscus, with which the author does not deal. In Group 2 the sub- 

 groups are classified by the shape of the vegetative cell. 



A. Sheaths containing ovoid cells. 



B. Elongated cells with rounded ends. 



C. Oblong cells with square end. 



D. Short square cells. 



Sphierotilus is associated with sewage pollution, but does not 

 usually occur in raw sewage. The degree of pollution may be 

 roughly estimated by the presence or absence of diatoms. It is a 

 strict aerobe. Morphologically it is identical with C. dichotoma. 

 The filaments, often anchored at one end to some stationary object, 

 consist of cells within a sheath. The sheath is a thick soft tube in 

 its early stage, later becoming harder. 



While the organism is growing vigorously the sheath may ex- 

 pand from the pressure of the rapid numerical increase of vegeta- 

 tive cells. 



Transverse septa from the sheath separate the cells during the 

 earlier stages of growth. 



Three or four cells without a visible sheath have been observed 



EXPLANATION OF PLATE XX.—conti7iued. 



Fig. 18. — Empty sheath. Showing hard, tube-like form of old sheath. 



,, 19. — Cells of Sphseiotilus C. Either projected en bloc from sheath, or nucleus 

 of a string which has not yet developed a visible sheath. 



,, 20. — Spiral-shaped fragment of Sphasrotihis B. This fragment is not ciliated 

 and is not motile. It is probably a short thread distorted and broken 

 adrift by adverse influences. It has the soft sheath of a young string 

 and the ends are closed. 



,, 21. — Sphasrotilus B. The effect of pressure in a partly hardened sheath. 

 The cells are turned on their axis, but cannot escape through the 

 cell-wall. 



,, 22.1 Ditto. Partial multiplication of thread. Due to pressure of growth in 



,, 23./ a fairly soft sheath. 



,, 24. — Sphcerotikis C. Duplication of threads inside the sheath, due to grow- 

 ing pressure. This sketch suggests the possibility of multiplication 

 by longitudinal fission under certain circumstances. Compare 22 

 and 23, which might also be explained by this means. 



,, 25. — Ditto. Pressure has occurred when the sheath was very soft, and 

 caused false dichotomy ; the sheaths have since hardened and partly 

 emptied. 



,, 26. — Sphffrotilus B. False dichotomy, due to pressure. The pressure is 

 continuing, and the sheath is not yet very hard ; a second cell is 

 slipping into the branch string formed by the first. 



„ 27. — Ditto. False dichotomy ; pressure relieved by branch formation ; sheath 

 still soft. 



