362 



SEWAGE AND SEWAGE DISPOSAL 



from a physiological viewpoint. They may roughly he divided 

 into four classes hydrolyzing, oxidizing, reducing and pathogenic. 

 Fuller gives the estimated constituents of average sewage as 

 follows: 



Grams per capita 

 daily. 



Parts per 

 million. 



Hydrolyzing Bacteria. Probably most of the early changes which 

 occur are hydrolytic, that is, the substance is caused to take up 

 water, becomes unstable, and for some reason falls into fragments, 

 thus often passing from a non-soluble compound of complex con- 

 stitution to a simple soluble substance. 



Protein liquefaction belongs to this type of changes and is brought 

 about by a great variety of bacteria working in conjunction with 

 each other. The proteins are hydrolyzed by successive stages to 

 proteoses, peptones, peptids, amino-acids and finally to ammonia, 

 carbon dioxid, methane, hydrogen, etc. It probably corresponds 

 in the main with the changes which have been considered under 

 ammonification. The final products vary widely, depending upon 

 whether the process is being carried on under aerobic or anaerobic 

 conditions. The tendency is for it to partake more of putrefaction 

 in the septic tank and decay in soil. 



