82 THE MANURE HEAP AND SEWAGE. 
that hastens the decomposition power of the bacteria so that they 
will rapidly destroy the organic products in the sewage. The 
method has not been devised by any one person, but has been the 
result of observations and experiments of several, extending over 
many years, and finally crystallized into practical results. 
The bacterial treatment of sewage depends upon the destructive 
action of the decomposition and putrefactive bacteria. Putre- 
factive bacteria decompose all kinds of organic bodies, both the 
nitrogenous and those purely carbonaceous. Most of the solid 
matter in the sewage is composed of these organic bodies, and it is 
evident that if the sewage can be induced to undergo a thorough 
decomposition under the action of microorganisms, this will produce 
a great effect upon the composition of solid matters present. 
Almost all of them will be reduced to simpler compounds. The 
carbonaceous material will be reduced eventually, if the process 
is complete, into CO 2 and water, with the liberation of hydrogen 
or perhaps marsh gas (CH 4 ). Such gases would leave the liquid 
and join the atmosphere, The nitrogenous material would suffer 
the decomposition, resulting in the production of ammonia; and 
denitrification, which would be sure to occur, would still further 
reduce this to free nitrogen. Such gases also would be sure to join 
the atmosphere unless held in solution in the liquids. In short, 
the putrefactive processes, which in the manure heap produce a 
loss deprecated by the agriculturist, would produce here exactly 
the result which the sanitary engineer desires to reach, a destruction 
and dissipation of organic material. 
Such changes will take place as readily in sewage as in manure 
or in the soil. Indeed, observation and analysis show that they 
commonly take place much more rapidly. In the first place, 
the organic matter to be acted on is generally in a soluble or partly 
dissolved condition, and very easily acted upon by bacteria. 
Secondly, the great abundance of water facilitates the action, for 
bacteria require an abundance of water for their best growth. Thirdly, 
the bacteria are present in extreme abundance. All sewage con- 
tains bacteria in large numbers, although naturally the number 
varies. A common sewage contains from 7,000,000 to 10,000,000 
