118 Bacteria in Relation to Country Life 



activities, and the septic tank has been accorded a 

 prominent role in the purification of sewage. 



Temperature and bacterial activities. — The low tem- 

 perature of the winter months seriously retards bacterial 

 activities. The rising temperatures of spring and summer 

 stimulate these activities to such an extent as to permit 

 the organisms to regain the lost ground. Some classes 

 of bacteria are more susceptible than others to cold 

 weather, yet all are retarded in their growth, as is proved 

 by the diminished efficiency of the bacteriological pro- 

 cesses in very cold weather. 



Warm countries offer favorable conditions for con- 

 tinuous and intense bacteriological development, and 

 permit the completion of the biological changes in a 

 shorter period. Due consideration should always be 

 given to the paramount influence of temperature in 

 the biological purification of sewage (page 120). 



Hydrolysis. — The anaerobic changes that take place 

 in the septic tank involve the breaking down of the 

 complex nitrogenous substances known as proteins, or 

 albuminoids. This transformation, which may be accom- 

 plished by a large variety of anaerobic ferments, is known 

 as hydrolysis. The nitrogen of the protein bodies is 

 changed to a large extent into ammonia and other 

 nitrogenous substances somewhat more complicated 

 than the latter, yet simple in composition as compared 

 with the proteins themselves. The non-nitrogenous 

 substances, including the starches, sugars, and cellulose, 

 are also decomposed and transformed, for the most part, 

 into gaseous products. On account of the absence of 

 atmospheric oxygen in the septic tank, these gases are 



