NUMBERS OF MICROORGANISMS 



47 



known. By using 26 plates and a series of dilutions (13) ranging from 

 ts to TFS.Vinrj the following results were obtained: 109 



For the examination of trophic protozoa, the soil sample is moistened 

 with some sterile water, placed on a slide and examined for a minute 

 under the microscope. 



When soil or soil suspension is placed in a medium favorable for the 

 development of protozoa, there is found a close connection between the 

 growth of these organisms to that of the bacteria, the former always 

 lagging behind. There is also observed a general sequence of protozoan 

 forms, the flagellates appearing first, followed by the ciliates and later 

 by the amoebae. A detailed review of the media used for the cultiva- 

 tion of protozoa is given elsewhere (p. 317). 



Garden soils contain a great number of protozoa; 110 amoebae were 

 found 111 to develop on agar plates, even when the inoculum was only 

 1 mgm. of soil. An average of about 100 ciliates and 1000 to 10,000 

 flagellates per gram of soil was reported by earlier workers. 112, m 

 Sherman 113 compared the numbers of protozoa in sixteen soils represent- 

 ing various soil types under various treatments; he found that normal 



109 Cutler etal., 1922 (p. 32). 



110 Hiltner, 1907 (p. 47). 



111 Stormer, K. Uber die Wirkung des Schweffelkohlenstoffs und ahnlicher 

 Stoffe auf den Boden. Jahresb. Ver. angew. Bot. for 1907, 5: 113-131. 1908. 



112 Rahn, 1913 (p. 45). 



113 Sherman, J. M. Studies on soil protozoa and their relation to the bacterial 

 flora. Jour. Bact. 1: 35-66; 165-185. 1916. 



U4 Waksman, S. A. Studies on soil protozoa. Soil Sci. 1: 135-152; 2: 363- 

 376. 1916. 



