668 CONTRIBUTIONS TO OUR KNOWLEDGE OF SOIL-FERTILITY, vi. 



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6 g 13 35" 4^:: ^7 09 S3 day 



These soils had not been heated, and do not show the rapid rise 

 tliat occurred in the earlier experiments. The curves of iv. a, for 

 the most part, rise fairly steadily, and there is little difference be- 

 tween them. We see no indication of any influence having been 

 exerted by phagocytic protozoa derived either from the un filtered 

 extract or from the untreated soil. Beyond the fact that Nos. 2, 3, 

 and 4 received originally more bacteria than the control, and conse- 

 quently obtained a lead, these tests practically give the same result. 

 The protozoa cannot be said to have any action upon the soil-bac- 

 teria at 28°, at which temperature they are very active.* 



The curves of the tests at 15° differ from those at 28°. Those 

 which received the extracts, gave a more rapid bacterial growth 

 within the first ten days, but, as at the higher temperature, there is 

 no pronounced evidence of protozoal activity. 



One of the points brought out, is the influence of temperature 

 upon bacterial growth. At 15° the numbers never rose above 15 

 millions, and remained constant between 10 and 15 millions per 



* The period of multiplication for Amcpha Umax was found to be If 

 hours at .37°, 8 hours at 28°, and 28 hours at 15°. 



