128 TRANSACTIONS OF THE 
THE INFLUENCE OF ARSENIC UPON THE BIOLO- 
GICAL TRANSFORMATION OF NITROGEN IN SOILS. 
By J. E. GREAVES. 
(Published in Biochemical Bulletin, Vol. III, (1913), 
pp. 2-16.) 
(Summary) 
The article represents a study of the effects of 
arsenic upon the bacterial activities of the soil and it shows 
that one hundred parts per million of sodium arsenate may 
be applied to a soil rich in calcium and iron without mater- 
ially decreasing the ammonifying and nitrifying powers of 
that soil. Smaller quantities may stimulate these activities. 
Zinc arsenite, lead arsenate, and arsenic trisulfide stim- 
ulate the ammonifying activities of a soil, and their toxi- 
city is not very marked until comparatively large quantities 
of arsenic are present. The two former reduce the am- 
monifying and nitrifying activities only one-half when 1,120 
parts per million of arsenic are present, while arsenic 
trisulfide exerts a stimulating influence upon the ammoni- 
fying activities of the soil in the lower concentrations and 
does not become very toxic even in the highest concentra- 
tions. 
Paris green exerts marked toxicity on the ammoni- 
fiers, even when present in small quantities. When present 
in large quantities it practically stops ammonification in 
soil. 
All these compounds stimulated nitrification, the stim- 
ulation being least for Paris green and greatest for lead 
arsenate. 
Arsenic trisulfide and Paris green, when present in 
large quantities, nearly stopped nitrification. 
Arsenic stimulated ammonification and nitrification, 
when it was present in soils in small quantities, but in very 
large quantities it was toxic. It is improbable, however, 
that lead arsenate, zine arsenite, or arsenic trisulfide, will 
ever be applied to agricultural soil in quantities sufficient 
