Bacteria and Sulfur 295 



to combine with oxygen to form water and subse- 

 quently, by causing the elementary sulfur deposited in 

 their cells to combine with oxygen to form, with water, 

 sulfuric acid. The last named combines with lime to 

 form sulfate of lime. The tissues of dead plants and 

 animals are made to give up their sulfur as sulfuretted 

 hydrogen by the common soil bacteria. The sulfuretted 

 hydrogen serves an important purpose in the life of a 

 special group of bacteria, and the sulfur finally reap- 

 pears as sulfate of lime, sulfate of magnesia, sulfate of 

 soda, or sulfate of iron, and is in a condition again to be 

 utilized by green plants. The transformation is thus 

 complete, and the sulfur is ready to pass through another 

 cycle and to circulate between land and sea. 



Sulfate of lime. — The drainage waters that pass out 

 of the soil contain considerable quantities of sulfate of 

 lime. The sea ultimately receives the latter as it re- 

 ceives all else borne to it from the land and offers it to 

 its denizens. Enormous quantities of gypsum are thus 

 brought to the ocean daily and are constantly being 

 added to by the restless streams. It should not be 

 supposed, however, that the gypsum that finds its way 

 to the sea is doomed to stay there unchanged and inert. 

 Other bacteria, widely distributed in nature, are capable 

 of compelling it to pass through other transformations 

 and to part with its sulfur. Some of the most common 

 decay bacteria, like Bacillus mycoides and Proteus 

 vulgaris have been found capable of producing sulfur- 

 etted hydrogen out of sulfate of lime and of thus chang- 

 ing once again the sulfur into a gaseous compound. 



Aside from the decay bacteria, there ^re well-define4 



