AGRICULTURE AND DENDROLOGY. 
17 
and before it is completed, rain may set in and carry the 
portion yet unconverted into the subsoil to a depth where 
the respective micro-organisms no more exist. The depth 
of the soil to which the conversion can be effected not 
being known was likewise subjected to an investigation, in 
which I was assisted by Mr. H. Yoshida. We took in 
calm weather samples of 50-60 grms. from different layers 
of the soil of the college farm, filled them at once into flasks 
previously sterilized by heat and closed with sterilized rub¬ 
ber plugs. After transporting them to the laboratory, we 
mixed them with 200 c.c. of a solution of urea sterilized by 
boiling, at the same time closing the flasks without delay. 
We are far from pretending that we succeeded by these 
measures in entirely preventing micro-organisms other 
than those of the soil from entering the vessels, but we 
believe, on account of our results, that we at least avoided 
essential disturbances, which would surely have taken place, 
if any considerable infection with atmospheric germs had 
occurred. We then drew small samples from the flasks from 
time to time, and determined the quantity of ammonia 
formed. The surface soil of a depth from 0-5 centimeters 
had the strongest effect ; between the 9th and 16th day of 
the digestion, the conversion of the urea was completed ; 
the sample from a depth of ‘25-30 centimeters the am¬ 
monification was likewise soon perceptible, but it continued 
very slowly and was not complete after 2 months ; earth 
from deeper layers than the preceding ones still contained, 
after 37 days, all the urea applied. In accordance with 
these results it may be safely assumed, that the capacity 
of soils imparted to them by micro-organisms for converting 
urea into ammonium carbonate gradually diminishes as the 
depth increases, and that it is practically nil in layers deeper 
than about 50 centimeters. In applying fresh urine far¬ 
mers would run the risk not only of damaging the crops 
but also of losing a more or less considerable part of the 
