4 Colorado Experiment Station. 
with reference to our soils, and consequently we are in a better position 
to recommend their use when such a practice becomes necessary. 
METHODS. 
In collecting the soil samples, every precaution has been taken 
to eliminate exterior contaminations. All surface debris was removed 
before opening up the soil, and all instruments and containers were 
thoroughly sterilized. Unless otherwise stated, the samples were taken 
to a depth of three inches; the soil in each case was removed with a 
sterilized spatula and placed in double, sterilized, paper sugar sacks. All 
samples were shipped by express to the bacteriological laboratory of the 
Experiment Station in order to minimize the time in transit, during 
which interval, if unduly prolonged, the soil flora might undergo 
changes. This statement is deemed necessary since many of the samples 
were taken more than five hundred miles from Fort Collins. Imme¬ 
diately upon arrival at the laboratory, each soil was spread out upon a 
sheet of heavy, sterilized, manilla paper and thoroughly mixed. It was 
next divided into two unequal portions*, the larger part being al¬ 
lowed to dry in the air in diffused light, while the remaining portion 
was transferred in a moist condition to a sterilized Mason fruit jar. As 
soon as the soils were air dry, which seldom requires more than twenty- 
four hours in our atmosphere, each was ground in a glass mortar, ster¬ 
ilized with mercuric chloride and subsequently rinsed with boiled, dis¬ 
tilled water, and passed through a thirty meash wire sieve. From each 
sample prepared in this manner, ten ioo-gram portions were weighed 
out, and eight of these were transferred to deep culture dishes, io x 4 
cm., similar to the ordinary Petri dish only deeper; the two remaining 
lots were analyzed at once for ammonia. A weighed amount of each of 
the four nitrogenous materials, employed to furnish the organic nitro¬ 
gen, corresponding to 100 m. g. of toal nitrogen was added to each of 
two 100 gram portions of soil. It was thoroughly mixed with the soil 
by constant stirring with a sterilized glass rod for five minutes. Each 
preparation was then inoculated with 10 c. c. of its respective soil in¬ 
fusion. corresponding to 5 grams of the fresh soil. The infusions were 
made by shaking 100 grams of undried soil with 200 c. c. of sterile, 
disti led water, and after allowing it to stand for thirty minutes for the 
coarser particles to settle, the required amount of the turbid suspen¬ 
sion was drawn off with a sterile pipette and distributed uniformly 
over the surface of the soil in the culture dish. In addition, each basin 
received sufficient sterile, distilled water to give the soil its optimum 
moisture content, approximately 20 per cent. Additional quantities of 
water were used for the organic matter at the rate of 1.5 c. c. for each 
gram of material. All of the cultures were kept in the incubator for 
seven days at a temperature of 28° - 30° C. At the end of this time, 
the contents of each dish were transferred to a copper distilling flask 
with 250 c. c. of ammonia—free water and distilled with 7 grams of 
heavy, calcined magnesia to liberate the free ammonia. The distillates 
were received in N/10 sulphuric acid and subsequently titrated with 
