TREATMENT OF CITY SEWAGE 87 
compounds are decomposed by bacterial action, a part of the 
resulting decomposition products going into the air as gas, and a 
part being built up, in the soil, into nitrates, to feed the growing 
crops. The offensive waste material is thus disposed of by being 
converted into inoffensive and useful products. Sewage farms 
thus prevent the sewage contamination of streams, harbors, and 
seaside resorts. ‘This in itself is sufficient to make this method of 
disposal a desirable one. 
But the appearance of certain practical difficulties has pre- 
vented a wide development of this system. It is, of course, im- 
possible to expect farmers to adopt this system unless it is profit- 
able, and, unfortunately, it frequently proves that such sewage 
farms are run at a loss instead of a gain. To be sure, in some 
places very favorable returns have been yielded, and largely in- 
creased crops have been reported. But in other places un- 
favorable reports have been made, and at the present time sewage 
farming is not increasing. Since the objections to it are purely 
practical, they may in time be overcome. The chief objections 
are as follows: (z) It is unhealthful to irrigate garden crops with a 
sewage that is sure to contain disease germs. ‘This objection 
applies chiefly to vegetable products which are eaten without 
cooking, like lettuce, celery, etc. (2) Land near the large cities is 
usually too valuable to be used for farming processes. If the farm 
is at some distance from the city the expense of carrying the 
sewage to it becomes so great as to make the undertaking a losing 
instead of a profitable one. (3) Only a fairly porous and partly 
sandy soil can absorb the quantity of sewage necessary for the 
disposal of the product. In order that the soil may absorb it, 
the sewage must be decomposed and nitrified by bacteria. If 
this nitrification does not occur, the soil becomes clogged with the 
sewage products. Hence, if the soil is heavy and contains much 
clay it cannot be used for sewage farming. While sewage farms 
are successful and profitable in the sandy soils around Berlin, they 
are not possible in many another locality where the soil is of a dif- 
