94 THE MANURE HEAP AND SEWAGE 
disease germs? So far as evidence goes to-day it seems that the 
typhoid bacillus is eliminated by the treatment, and the effluent 
from such beds fails to show typhoid bacteria, even when they have 
been purposely put in the sewage. Bacteriologists who have had 
confidence in the efficacy of the purification have not hesitated to 
drink freely of the water from such a sewage filter bed. It is 
certain, therefore, that the treatment greatly improves the 
healthfulness of the sewage. But that it removes all danger from 
it cannot be positively stated. 
Such a disposal of sewage means, of course, a complete loss of 
the nitrogenous material, for no method is adopted for utilizing the 
wasted nitrates. But this fact is no longer regarded so seriously as 
it was a few years ago. We have learned that there are efficient 
forces in nature for bringing back from the atmosphere the nitrogen 
dissipated from the soil, and it is a matter of less significance to 
throw away the sewage nitrogen than it appeared to be when the 
only known source of nitrogen was supposed to be the fixed nitro- 
gen of the soil. Since the soil can readily replace its lost nitrogen 
through the agency of certain species of bacteria (see Chapter VII), 
it is no serious matter if some of the nitrogen is thrown away. 
TREATMENT OF FARM SEWAGE 
Upon the ordinary farm the sewage problem is rarely of any 
importance, because of the small amount of material. The wastes 
which form the sewage in the city are kept separate on the farm 
and are not all treated alike. Part goes to the manure or compost 
heap, and later is returned to the soil with the manure. Part goes 
to the privy vault and is handled like manure; while still another 
part drains from the sink and is generally allowed to waste itself 
on the ground. A considerable portion of city sewage, like the 
refuse from factories, etc., has no counterpart on the farm. 
Nothing further need be said concerning the first of these por- 
tions. The contents of the privy vault have practically the 
same relations to bacterial decomposition and denitrification as 
