164 MISSOURI BOTANICAL GARDEN. 
earlier, this difference, at least so far as initial effect is 
concerned, may be due to the time at which analyses were 
made, the process of evaporating the substance having 
been shown to decrease the number of bacteria from 50 to 
75 per cent. The apparent correlation between the quantity 
of chemical required to give a marked decrease in protozoa 
and the quantity required to give a subsequent increase in 
bacteria would appear to support the theory of Russell and 
Hutchinson. This supports with equal strength, though, 
the theory of Greig-Smith (34) for an increase in quantity, 
within limits, would effect an equally increasing solution 
of toxic substances. 
So far as the writer is aware, no one has reported a stimu- 
lative effect of small quantities of such chemicals (acting 
in soil) upon number of bacteria, but in the light of Fred’s 
recent work such is not at all surprising. He has shown, 
beyond a doubt, the stimulative effect upon certain soil 
organisms when in a liquid medium. And while the quan- 
tities acting as a stimulant in soils are much greater than in 
liquids, in the light of the work of Lipman, and Stevens 
and Withers (35) this is not surprising, as they have shown 
that the activities of a complex soil culture in soils may be 
decidedly different from the activities of the same culture 
in liquid. 
This stimulative effect may or may not be evident under 
greenhouse and field experimental conditions. If evident, 
the increase occasioned by it is soon lost. If the theory of 
Russell and Hutchinson be correct, the above contradictory 
results are easily explained, for in no case, under greenhouse 
and field experiments, have the chemicals studied exerted an 
appreciable effect on the protozoa, and in laboratory experi- 
ments, not with the quantities used (.2%) by these investi- 
gators (see Tables VI, VII, VIII, and IX). 
Measuring the effect produced upon the total number of 
bacteria by the crop yield, greenhouse experiments have 
given negative results. In Table VI it is shown that, fol- 
lowing applications far exceeding any field experiments 
thus far reported, no increase in bacterial content was 
