INTRODUCTION ■ 3 



accumulations that contain organic matter, is one that is 

 important, and is in some instances considerably influenced 

 by the activities of the sulphur bacteria. The stench of 

 black muds on the foreshore and the pollution which attends 

 the heaping together of mud, sand, and organic matter on our 

 shores cannot be neglected. Among the factors which must 

 be reckoned with are the activities of the sulphur bacteria. 

 Again, some of these organisms develop freely in sewage- 

 contaminated water, and may be utilized in the detection of 

 sewage contamination in water supposed to be sewage free. 

 The sulphur bacteria abound in sulphur wells, and although 

 they do not produce the salts which give such wells their real 

 or alleged healing qualities, inasmuch as they multiply freely 

 in such waters, the nature of the products of their metabolism 

 is of interest to those who consume the water. 



Connotation of the Term " Sulphur Bacteria." 



The list of bacteria that effect changes in sulphur com- 

 pounds is a fairly comprehensive one. The changes include 

 oxidation processes as well as reduction processes. We may 

 represent the nature of the changes as follows : — 



Sulphide ^ Sulphur ^ Sulphate. 



Thus complete oxidation as w^ell as complete reduction 

 of the sulphur element may be effected. The term sulphur 

 bacteria embraces only those organisms which oxidize the 

 HgS to S, store the latter temporarily in their bodies, and then 

 oxidize it to SO4. The term is thus used in a restricted 

 sense, for there are other bacteria which bring about chemical 

 changes in sulphur compounds. Thus we have : — • 



1. Thionic Acid Bacteria or Thiosiilphate Bacteria, which 

 oxidize thiosulphates to tetrathiosulphates and sulphates in 

 accordance with the equations 



SNa^SaOa + 50= aNa^SO^ + Na^S^Oe, 

 NagSgOa + = Na2S04 + S. 



2. Denitrifying Thiosiilphate Bacteria, which effect the 

 oxidation of sulphites, thiosulphates, sulphuretted hydrogen, 



