d in the value of the nitrogen the
soil contained before using. Soil, on a farm, is cheap.

It is clear from these facts that any earth-closet manure a farmer would
be likely to purchase in the city has not a very high value. It is
absurd to talk of making "guano" or any concentrated fertilizer out of
the material from earth-closets.

"It is rather a reflection on our science and practical skill," said the
Doctor, "but it looks at present as though the only plan to adopt in
large cities is to use enormous quantities of water and wash the stuff
into the rivers and oceans for the use of aquatic plants and fishes. The
nitrogen is not all lost. Some of it comes back to us in rains and dews.
Of course, there are places where the sewage of our cities and villages
can be used for irrigating purposes. But when water is used as freely as
it ought to be used for health, the sewage is so extremely poor in
fertilizing matter, that it must be used in enormous quantities, to
furnish a dressing equal to an application of 20 tons of stable-manure
per acre."

"If," continued the Doctor, "the sewage is used merely as _water_ for
irrigating purposes, that is another question. The water itself may
often be of great benefit. This aspect of the question has not received
the attention it merits."

PERUVIAN GUANO.

Guano is the manure of birds that live principally on fish.

Fish contain a high percentage of nitrogen and phosphoric acid, and
consequently when fish are digested and the carbon is burnt out of them,
the manure that is left contains a still higher percentage of nitrogen
and phosphoric acid than the fish from which it was derived.

Guano is digested fish. If the guano, or the manure from the birds
living on fish, has been preserved without loss, it would contain not
only a far higher percentage of nitrogen, but the nitrogen would be in a
much more available condition, and consequently be more valuable than
the fish from which the guano is made.

The difference in the value of guano is largely due to a difference in
the climate and locality in which it is deposited by the birds. In a
rainless and hot climate, where the bird-droppings would dry rapidly,
little or no putrefaction or fermentation would take place, and there
would be no loss of nitrogen from the formation and escape of ammonia.

In a damper climate, or where there was more or less rain, the
bird-droppings would putrefy, and the ammonia would be liable to
ev