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166 MISSOURI BOTANICAL GARDEN. 
' Similar negative results have been reported by many 
investigators. 
Thus far, no method has been devised whereby the total 
number of protozoa can be determined; but, from observa- 
tion of hundreds of samples, the total number of the differ- 
ent types seems to be very small in normal soils. The 
method used affords ample time for multiplication, and still 
the examination of 10 cc. of the supernatant liquid of a 
twenty-four-hour-old water culture (50 parts soil to 100 
parts water) often reveals less than twenty-five organisms. 
When we take into consideration the low water content so 
often present in our soils, with the necessarily thin films 
of water and the small number of comparatively large 
organisms that must cover this soil, the assumption seems 
unfounded that such organisms prevent the multiplication of 
bacteria. In fact, computing the diameter of the theoretical 
water pore of a medium soil by Slichter’s (37) formula, we 
find that for protozoa to pass through the soil they must pass 
through holes the diameter of which is many times less 
than the diameter of their bodies. While the writer does 
not wish to imply that it is in practice impossible for these 
flexible organisms to move about in the soil, he does wish 
to call attention to the fact that with the relatively few 
active organisms present, the physical conditions of the soil 
must render their coming in contact with a majority of 
soil bacteria highly improbable. Furthermore, the recent 
work of Goodsey speaks strongly against the existence in 
soils of protozoa in the active condition, at least under 
normal conditions. If this be true, their effect upon the 
bacterial content of the soil is nil. Under the conditions 
cited by Russell and Gadding (38), it seems possible that 
protozoa might become sufficiently numerous to produce an 
appreciable effect, but this is only an isolated abnormal 
condition. 
After the body of this article had been written and con- 
clusions drawn, the writer noted with a great deal of pleasure 
the following conclusions drawn by Emmerich, Leinigen 
and Loew (40), after investigating the same problem: 
