Sewage and Sewage Effluents. 201 



Plainfield, N. J., the seeding of a tank with cesspool 

 contents has produced a material improvement in septic 

 action. 



Knowledge of the kinds of bacteria involved would 

 make it possible to substitute scientific control for such 

 empiricism and might well lead to improved methods of 

 a more intensive character than are yet available. The 

 work already done upon a laboratory scale furnishes 

 promise of such results. The student who wishes to 

 follow out this line of investigation will find a good sum- 

 mary of what is already known of the hydrolysis and 

 denitrification of nitrogenous bodies and the decomposi- 

 tion of cellulose and other carbohydrates in Rideal's " Sew- 

 age, and the Bacterial Purification of Sewage " (1906). 



Gage (1905) has made a suggestive study of the bac- 

 teria which carry on the reducing changes in sewage 

 which deserves the study of all who are interested in the 

 more theoretical aspects of sewage treatment. His method 

 consisted in plating sewages and effluents, isolating typi- 

 cal cultures and determining their power to decompose 

 peptone and nitrates with the production of ammonia 

 and free nitrogen. The rate of gelatin liquefaction, the 

 amount of nitrate reduced, the amount of free ammonia 

 formed, and the amount of nitrogen liberated were quan- 

 titatively determined for each culture thus isolated. 



The numerical values obtained, multiplied by the num- 

 ber of bacteria, apparently of the same type, observed in 

 the plates, gave coefficients of the liquefying, denitrifying, 



