214 MICROBIOLOGY OF WATER AND SEWAGE. 



part of the same molecule. The energy released in this process is utilized 

 in the vital functions of the organism. This action is neither oxidation 

 nor reduction, or more strictly, it is both taking place simultaneously. 

 A good example of such a process is the fermentation of urea. The 

 reaction takes place as follows: 



CO(NH 2 ) 2 +2H 2 0=(NH 4 ) 2 CO S . 



Carbon is oxidized at the expense of hydrogen, a process which, by itself, 

 is endothermic, that is, requires heat or energy for its maintenance. But 

 the heat of formation of the final product is greater than that of the initial 

 substances and the energy thus liberated becomes available for use by 

 the bacteria. It is in this way that hydrolytic changes of this character 

 play the same role in anaerobic reactions that is played by direct oxida- 

 tion under aerobic conditions. 



The Liquefaction of Protein. One of the most clearly defined and 

 useful types of bacterial activity to be seen in the various sewage disposal 

 processes is that which we term liquefaction. This term is used to denote 

 broadly all those changes by which solid and insoluble organic matter is 

 converted into a soluble condition. The particular process known as 

 protein liquefaction is in the main analogous to gastric digestion. Its one 

 characteristic is the increased solubility of the product. The practical 

 importance of protein liquefaction in sewage disposal is very great and the 

 value of the liquefying bacteria correspondingly high. Nevertheless, 

 aside from our knowledge of analogous processes in digestion and in 

 bacterial putrefaction of albuminous substances, we know almost nothing 

 of the chemistry or the bacteriology of this process. An enormous 

 variety of bacteria are included in this group. The whole process is 

 doubtless the result of a very complicated symbiosis in which various sub- 

 groups of bacteria carry out the initial reaction, from which point other 

 groups carry it through successive stages. Absence of one or another of 

 these groups or of some important species of any group doubtless accounts 

 for the diverse results that are recorded. It is well known that the activi- 

 ties within a septic tank, for example, are seldom twice the same. Gross 

 differences readily apparent to the senses of one versed in such matters 

 certainly exist, and in actual results it is rare to find two tanks doing 

 exactly the same kind of work. Much depends of course upon the chem- 

 ical character of the sewage itself, but much, that is still unexplained, must 

 eventually be traced to the great diversity of the sewage flora and the com- 



