STUDIES ON SOIL PROTOZOA 45 



strated the presence of active protozoa. Under these con- 

 ditions, as was pointed out by Goodey, many protozoa may 

 become active. When we consider the minute size of these 

 organisms it would appear obvious that they may become active 

 whenever the soil is in a saturated condition. Martin (1913) 

 by means of a special method which he has developed has been 

 able to prove definitely that soil contains active protozoa. Cun- 

 ningham (1914) has collected data which indicate that some of 

 the protozoa exist in soil in the active state. 



Experimental 



In order to see if any of the soil protozoa are active, the 

 following experiment was performed. Four pots each contain- 

 ing two kilograms of sterilized soil with an optimum moisture 

 content of about 17 per cent were inoculated with two grams each 

 of a normal soil, which showed 10,000 protozoa per gram by the 

 dilution method. These pots were then brought up to varying 

 moisture contents by the addition of sterile water, as follows: 



per cent 

 H2O 



Pot No. 1 11 



Pot No. 2 12 



Pot No. 3 15 



Pot No. 4 22 



Since one gram of normal soil, with a protozoal count of 10,000 

 per gram, was used to inoculate 1,000 grams of sterile soil, the 

 resulting mixture should contain, approximately, only 10 of these 

 organisms per gram. After fifteen days incubation at 20 to 25°C., 

 these pots were sampled, and in every case flagellates were found 

 in the 1/10,000 dilutions. This could not be explained except on 

 the assumption that these animal organisms had undergone 

 rapid multiplication. The forms found in greatest numbers in 

 these pots were the same forms which were noted as the pre- 

 dominating types in normal soils. Monas sp. did not occur 

 in the 1/10,000 dilution cultures from the soils containing only 

 11 and 12 per cent moisture. In the case of pot 4, with a mois- 

 ture content of 22 per cent, Colpoda cucullus was found in the 



