CHAPTER XI. 



THE SULPHUR-BACTERIA. 



§ 1. INTRODUCTION TO SULPHUR-BACTERIA. 



The Sulphur-bacteria perform excellent service in nature, for, by 

 their aid, substances absolutely useless in themselves for plant life 

 are changed into substances y^hich can again be used up by plants. 

 As has been explained, a large number of bacteria have the power 

 of breaking up albuminous materials, with the result that the 

 sulphur bound up in their molecules escapes as sulphuretted hydrogen 

 {H2S). The decomposition of eggs is a good example of this action. 

 The emanation of sulphuretted hydrogen can easily be tested by 

 holding a piece of lead paper above some decomposing liquid, when 

 the paper will turn black if this gas be given oflF. This property 

 of decomposing albuminous substances, with evolution of HgS, is 

 common to almost all bacteria which feed on these substances. This 

 gas may also arise in a variety of other ways, thus sulphates may 

 be reduced to the sulphide by such bacteria as Vibrio hydrosulfureus, 

 Proteus vulgaris and others : again, thiosulphates may be changed, 

 with formation of sulphuretted hydrogen, by Vibrio hydrosulfureus 

 and other bacteria, and, according to Beijerinck, sulphites also may 

 be reduced in the same way under similar conditions. As is to be 

 expected, therefore, a large quantity of sulphuretted hydrogen is 

 being produced daily, as the result of this decomposition, and the 

 places in which the sulphur-bacteria are to be found are just those 

 waters in which sulphuretted hydrogen is present. They are there- 

 fore principally found in sulphur springs. They form a delicate 

 matting to the bed of the spring, the matting being most commonly 

 snow-white, but sometimes red or reddish-violet. They are best 

 studied late in autumn or at the beginning of the year, when the 



