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Hillhousia mirabilis, a Giant Sulphur Bacterium. 

 By G. S. West, M.A., D.Sc., F.L.S., and B. M. Griffiths, B.Sc. 



(Communicated by J. Bretland Farmer, F.R.S. Eeceived July 7, 1909.) 



[Plate 9.] 



The organism which forms the subject of this paper has been under the 

 observation of one of us for a number of years, but its true nature was not 

 immediately recognised. It has been found in various parts of England and 

 Ireland since 1892, always occurring in very stagnant pools and marshy bogs. 



Until quite recently it was only found very sparingly amongst Algse, 

 Infusoria, etc., generally in situations where there was much decomposing 

 organic matter. During the past winter, however, the organism has been 

 found in abundance in the mud of the shallower part of an old pool in 

 Worcestershire. This has enabled us to make cultures of it, and to make 

 a study of its general biology and structure. We have named it Hillhousia 

 mirabilis* 



The cells are solitary but gregarious, occurring freely among other 

 organisms and numerous small particles of decaying organic matter. They 

 secrete very little or no mucus, even in a culture, so that colonies are not 

 built up. 



They are for the most part shortly cylindrical, with hemispherical ends, 

 and are usually straight. Some individuals exhibit a very slight curvature, 

 and others may be observed which are slightly attenuated towards each 

 extremity. The cells are from one and three-quarters to three and a-quarter 

 times as long as broad. 



For a unicellular bacterium the dimensions of this organism are 

 phenomenally large. The diameter of the cell varies from 20 to 33 fi, and 

 averages about 26 //,. The length varies from 42 to 86 fi, and averages 

 about 60 ft. 



In its normal healthy condition the cell is packed with globules of oily 

 amorphous sulphur of various sizes, the largest of which have a diameter of 

 about 10 ix (Plate 9, figs. 1 to 3). These globules are very crowded, and, 

 when isolated, are seen to be somewhat irregular, although rounded (fig. 17). 

 Their refractive nature gives the organism almost a black appearance under 



* The generic name " HiWwusia" has been given in honour of Prof. W. HiJlhouse, the 

 retiring Professor of Botany in the University of Birmingham, to whom both authors owe 

 much in the way of kindly advice and criticism. 



