X-axis: Feby. Feby. April
Y-axis (left): Amoebae Active numbers per gramme of soil
Y-axis (right): Bacteria millions
Legend: Dimastigamoeba
Species α
Bacteria
In the case of the bacteria, however, the agent causing the fluctuations is mainly the active amœbæ. This was well shown during the year’s count, for with only 14 per cent. of exceptions, 10 per cent. of which can be explained as due to rapid excystation or encystation, a definite inverse relationship was established between the active numbers of amœbæ and the number of bacteria ([Figs. 11] and [12]). Thus a rise from one day to the next in the amœbic population was correlated with a fall in the numbers of bacteria and vice versa. It must not be supposed that the flagellates are of no account in this process; some species, known to eat bacteria, undoubtedly induce slight depressions, but, owing to their small size, any effect is masked by the greater one of the amœbæ.
Fig. 12.—Numbers of active amœbæ (Dimastigamœba and Species α) and bacteria in 1 gram of field soil for typical periods in September, October, and November, 1920.
X-axis: August September October
Y-axis (left): Amoebae, thousands
Y-axis (right): Millions, Bacteria