HYDROGEN ION CONCENTRATION OF PROTOZOAN CULTURES. 75 



FIG. i. Top Curves show the Ph of soil and ordinary hay infusion cultures 

 for a period of over 3 months. 

 A = soil culture, prepared with soil, hay infusion, tap water and inoculated with 



organisms. 



B = culture prepared with hay infusion, tap water and inoculated with organisms. 

 Space between arrows indicates time when organisms appeared to be most 

 abundant. 



Bottom Curves show the Ph of cultures with and without hay and also the Ph 

 of inoculated and non-inoculated cultures. 



C = culture prepared with hay infusion, tap water and inoculated with organisms. 

 D = culture prepared with filtered hay infusion and tap water and not inoculated. 

 E = culture prepared with hay, filtered hay infusion and tap water and not in- 

 oculated. 

 F = culture prepared with boiled hay, hay infusion, tap water and inoculated with 



organisms. 

 G = culture prepared with boiled hay, filtered hay infusion and tap water and not 



inoculated. 



Volume of culture, 5 liters. Abscissas, time in days indicated. Ordinates 

 represent Ph. 



stituents of the hay. The differences in Ph between inoculated 

 and non-inoculated cultures are probably due, either to a reduc- 

 tion of the bacteria by the protozoa, or possibly to various 

 excretion products of the protozoa themselves. 



It is also of interest to point out here that in the soil cultures 

 there is a relatively short period of acidity followed by a longer 



