186 CONTRIBUTIONS TO OUR KNOWLEDGE OF SOIL-FERTILITY, xvi,, 



droplet of soil-suspension. The latter were thus controls. The 

 amoebEe-cultures were twice seeded with amcebse, once, at the 

 start, and again on the second day, as the first seeding did not 

 seem to have been successful. They grew slowly at 18"^ and 

 exhibited a twenty-fold increase on the tenth day, and a fifteen 

 and ten-fold increase on the thirteenth day with the humic acid 

 and humic acid -|- soil respectively. They were tested on the 

 fourteenth day. 



The addition of soil to the culture-fluids had no influence, one 

 way or the other, in increasing or decreasing the numbers, and 

 its use appears to be of no value. The experiment shows pretty 

 clearly that any toxic effect is not caused by the amcebse, but 

 rather by the bacteria which always accompany the protozoa. 

 It is doubtful if the alkalinity, as indicated by methyl-orange, is 

 a true index, but, if accepted as true, the neutralised solutions 

 were certainly more nutritive than the unneutralised, for the 

 nnmbers were higher. With a better indicator, a lower reaction 

 might have been obtained and higher numbers furnished in the 

 neutralised tests. At any rate, it is pretty safe to conclude, that 

 the rise in numbers upon dilution is largely, if not entirely, due 

 to the lesseninof of the alkalinity of the filtered extracts. 



Reaction-Experiments. 

 The reaction of the soil-extract is never constant, but varies 

 from day to day. probably within certain limits. For example, 

 an extract was made on November 30th, 1917, by taking 300 



