104 



PHYSIOLOGICAL ACTIVITIES 



The. oxidation of H2S to free S may be an explanation of 

 the origin of the great deposits of sulphur which occur in 

 Louisiana and along the Gulf coast. These deposits occur 

 in the same general regions in which natural gas and oil 

 occur. The sulphur might have been derived from the same 

 organic material carried down by the Mississippi which 

 yielded the oil and gas. 



A purposeful utilization of the oxidizing power of bacteria 

 is in "contact beds" and "sprinkling filters" in sewage dis- 

 posal works. In these instances the sewage is thoroughly 

 mixed with air and brought in contact with large amounts 

 of porous material so as to expose an extensive surface for 

 oxidation (Fig. 72). 



Fig. 73. — One of the University hot beds. 



PRODUCTION OF HEAT. 



A direct result of the oxidizing action of bacteria is the 

 production of heat. Under most conditions of bacterial 

 growth this heat is not appreciable. It may become well 

 marked. The "heating" of manure is one of the commonest 

 illustrations. The temperature in such cases may reach 

 70°. The heating of hay and other green materials is due 

 chiefly to bacterial action. This heating may lead to " spon- 

 taneous combustion." The high temperatures (60° to 70°) 

 favor the growth of thermophil bacteria which cause a still 

 further rise. The heat dries out the material, portions of 



