BY R. GREIG-SMITH. 



177 



In one test, a small amount of sodium phosphate was added to 

 the hay-infusion, but, from the appearance of the amoeba?, the 

 salt seemed to have enhanced the alkaline effect, at any rate it 

 favoured bacterial growth and rapidly destroyed the amoebae. 



The neutralisation of the alkalinity with lactic acid proved to 

 be useless, for, in three days, the culture was as alkaline as 

 before the addition. 



The advantage to be gained by using insoluble humic acid or 

 soil was tested with solutions obtained by diluting a 1% infusion 

 of hay with nine volumes of water, that is they contained one 

 part of hay per thousand. 



Experiment xxii. 



The tests were started with 500 c.c. of 0T% hay-infusion, either 

 a small quantity of washed humic acid (about 0-03 gram) or 25 

 grams of sterile soil and 10 c.c. of an amoeba-culture. The latter 

 represented from 30,000 to 50,000 mobile forms as estimated by 

 the counts of later starter-cultures. The amoebae in the earlier 

 periods were not counted, but they grew well, and a count made 

 on the sixteenth day showed 10,000 per c.c. in the humic acid, 

 and 5,600 in the soil test. On the twenty-fourth day, the flasks 

 contained 6,600 and 3,600 per c.c. respectively. 



The results show a low reaction, and it was assumed that the 

 fluids were approximately neutral. The humic acid tests do not 



