666 CONTRIBUTIONS To OUIt KNOWLEUCiE OF SOlI.-FKKTlLlTY.vi. 



miiltipliciitiun oi' bacteria occ-urs in the presence, as in tlie absence 

 of amcebae. 



In the ai)parent absence of protozoal activity in these experi- 

 ments, it seemed necessary to confirm some of Russell and Hutchin- 

 son's results. The most telling of their experiments was one in 

 which, as the result of adding a filtered suspension to a toluened 

 soil, tlie bacteria rose from GG millions on the 20th, to IGG millions 

 on the sixtieth day. No test was, however, made witli the until- 

 tered as against the filtered suspension. The experiment was not 

 confirmed, and, as it is jjossible that the results miglit have been 

 abnormal, a repetition of a certain portion of it was decided upon. 



An alluvial soil was air-dried, and treated for two days with o% 

 chloroform. After tlie evaporation of the solvent, a number of 

 20 grm. portions were weiglied out into small bottles, and mois- 

 tened with 4 c.c. of water or extract, a i^roportional quantity of 

 water being added to the tests which received the gram of air-dried, 

 untreated soil. The amount of water lost by evaporation was cal- 

 culated weekly or biweekly from the loss of weight of eight bottles, 

 two from each set, and the loss was made good. The moisture in 

 the soils varied up and down from 19-6 to 15-4. The extract was 

 made by sliaking 100 grm. of soil with 500 c.c. of water for 20 

 minutes, and filtering half of it through five inches of tightly 

 packed, cotton wool. This removed the larger protozoa, such as 

 Colpoda cucullus, but the cysts of smaller ciliates were not retained, 

 as was shown by their gi'owth in bean-infusion. The experiment 

 Avas made in duplicate, one set being incubated at 28°, the other at 

 15*. 



Experiment iv., a — The Addition of Soil and its Extracts. 



