OXIDATION OF SULFUR IN THE SOIL 235 



lum agilissimum isolated from river mud in Gratz which measures 

 about 6 to 10 by 1.8 to 2/n, of a rapid motiUty,and filled with black 

 sulfur granules; Chromalium cuculliferum which is round to 

 slightly elhptical, 6 by 4^, of a slow motiUtj^, with black, shining, 

 sulfur drops alwaj'S found in one pole, with one flagellum on the 

 granule-free pole. This form was found in a rotting mass of 

 algae in the garden basin at Gratz. Gicklehorn also described 

 three more forms: Microspira vacillans, Pseudomonas bipundata 

 and Pseudomonas hyalina, observed in the slime of the large basin 

 in the botanical garden at Gratz, which he classified with the 

 colorless sulfur bacteria. It must be noted here that none of the 

 forms studied by Gicklehorn were cultivated in pure culture, 

 which is true of most of those studied by the other investigators. 



The third group of the sulfur oxidizing organisms is found 

 among the purple bacteria. These are distinguished from the 

 sulfur bacteria described above by the production of a red, red 

 \'iolet or red brown pigment which is unevenly distributed 

 throughout the cell. In addition to the red pigment (bacterio- 

 purpurin), there is also present in all these bacteria a green pig- 

 ment (bacterio-chlorin). These bacteria are found abundantly 

 in sulfur springs and in mud waters. Not all the purple bacteria 

 are able to utilize hydrogen sulfide. Mohsch (1907) succeeded 

 in cultivating some of them in pure culture, but not the sulfur 

 forms. The role of sulfur in the metabolism of purple bacteria 

 is still an open question, since, according to Nadson (1903) and 

 Molisch (1907), the hydrogen sulfide is not required for nutrition 

 and sulfur is not accumulated. These results are in direct 

 opposition to the earlier ideas of Winogradsky (1888) and others. 

 A detailed study of the purple bacteria is found in the work of 

 MoUsch (1907). 



The fourth group of sulfur bacteria includes colorless organisms 

 that do not accumulate sulfur within their cells. These were 

 first demonstrated by Nathanson (1903) in sea water, and were 

 found to be able, by means of oxidation of hydrogen sulfide or 

 sodium thiosulfate, to reduce carbonic acid and construct from 

 it organic substances. By using a medium consisting of 3 per 

 cent NaCl, 0.25 per cent MgCl2, 0.1 per cent KNO3, 0.05 per cent 



