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







6 9 13 35" 4^i 5T 69 . S3 doyo 



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

 that occurred in tlie 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 unflltered 

 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 jironounced evidence of protozoal activity. 



One of tlie 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 Atmrha Umax was found to be ]f 

 hours at .37°, 8 hours at 28°, aii.l 28 hours at 15°. 



