5 1 6 Journal of Agricultural Research voi. iv. no. 6 



EFFICIENCY OF THE METHOD 



Upon examining the foregoing data, it is seen that the variation in 

 weights of successive amounts transferred from a solution at a given 

 temperature is very slight, the greatest variation being not more than i 

 per cent. 



In applying the improved loop method all calculations are based upon 

 distilled water at 22° C, or room temperature, as a standard. Hence, a 

 correction must be made when solutions of different surface tension are 

 employed, as the amount of culture solution transferred by the standard 

 loop would vary with the liquid. This is noted in Table I in comparing 

 the amount of distilled water, hay infusion, blood extract, and soil extract 

 transferred with the same loop. 



In order to facilitate calculations, i gm. of distilled water at 22° C. was 

 used as the standard to represent i c. c. 



Upon examining Table II, it is noted that the error incurred on account 

 of the variation in the density of solutions used is practically negligible. 



Where the number of organisms per cubic centimeter is relatively 

 small, the experimental error incurred in counting all the organisms con- 

 tained in the loop is 6.74 per cent, as seen from Table III. As shown in 

 Table IV, when the number of organisms per cubic centimeter is greater 

 and all the organisms in the loop are counted, the error is smaller. In 

 counting relatively small numbers of organisms in several fields of a 

 specially ruled slide the experimental error is greater in proportion than 

 if the organisms of the entire loop are counted, as shown in Table V. 



SUMMARY OF PART I 



(i) While the improved loop method is by no means devoid of errors, 

 it has proved much more satisfactory than any of the other above-men- 

 tioned methods. 



(2) It makes possible the quantitative study of the development of 

 organisms in solutions without greatly altering the culture solutions. 



(3) It is comparatively simple and requires but little time for any 

 single determination. 



(4) The improved loop method requires additional calculation because 

 corrections must be made when culture solutions of different surface ten- 

 sion than distilled water at 22° are employed, which is not the case when 

 the volume is always constant. 



(5) The average experimental error is about 7 per cent. 



II.— PROTOZOA OF GREENHOUSE SOILS 

 INTRODUCTION 



That small organisms other than bacteria, fungi, algae, and worms — 

 i. e., protozoa — exist in rich soils was known by Ehrenberg (5) as far back 

 as 1837. Greef (9) in 1866 recorded the presence of very large living 



