482 
Journal of Agricultural Research 
Vol. V, No. n 
found in the living condition, while in soils of very open structure where 
little or no surplus water is available they would seldom, if ever, be¬ 
come active. This point requires further investigation. 
The question at once arises, How are protozoan cysts transported to 
the different soils ? This process is likely to be brought about by wind 
action, by flowing water, and by mechanical means in the case of culti¬ 
vated soils. Likewise, if the protozoa do not exist in the active state 
in the soil, can they and do they multiply ? Under certain abnormal con¬ 
ditions of moisture they will become active and remain active as long 
as there are sufficient moisture and food and the absence of toxic or 
decomposition products. During this period multiplication takes place. 
When the conditions become unfavorable, no doubt some die, while the 
greater number encyst until conditions again become favorable for them 
to become active. 
EFFECT OF MOISTURE ON THE ACTIVITY OF PROTOZOA IN THE SOIL 
UNDER CONSTANT AND VARIABLE TEMPERATURES 
Large samples of three soils which had previously been used by the 
writer (i) in his study of protozoa were collected. The first was a 20 
per cent manure shale, greenhouse soil, the second, a clay loam orchard 
soil which had received no applications of manure for the last 20 years; 
and the third, a sandy loam field-plot soil that for a period of 20 years 
had been receiving annual applications of manure at the rate of 20 tons 
per acre. (Hereafter throughout this study the first soil will be desig¬ 
nated as the “greenhouse soil,” the second as the “orchard soil,” and 
the third as the “field soil.”) The soils were air-dried at laboratory 
temperature and then sieved through a 20-mesh sieve. The optimum 
moisture content of these soils was determined. Twenty 50-gm. portions 
of each soil were weighed into 4-ounce bottles. With each soil one series 
of five samples was left air-dried. To one series sufficient sterile tap 
water was added to make the moisture content half of the optimum. 
To another series enough water was added to increase the water content 
to the optimum. To a fourth series sterile tap water was added so that 
the resulting mixture would be equivalent to one and a half of the opti¬ 
mum. At one and one-half of the optimum the soils could take up all 
the moisture without any free water being present. The soils were well 
mixed with a stirring rod, so that the moisture content was homogeneous 
throughout. In order to prevent condensation on the sides of the 
bottles, they were left unplugged. The flasks containing four samples 
of each soil, representing four moisture contents, were incubated at 5 0 
to 7 0 C., one series at 15 0 to 17 0 , one at 22 0 to 24 0 , one at 32 0 to 33 0 , 
and one at the outdoor temperature. The samples were weighed daily, 
and the slight amount of moisture lost by evaporation was replaced. 
Each sample of soil was then examined for active protozoa not fewer 
