CHEMICAL STIMULATION OF GROWTH OF ASPERGILLUS NIGER 365 
We note that the growth with either zinc or iron salts alone is sharply 
limited even with concentrations that may physiologically be termed very 
high. The presence of free acid in the cultures to which the iron salts 
are added, while it does cause accelerations of growth, can not in view of 
their limited magnitude be held as the factor responsible for the results 
with the treated solution. Again we note also that there can be no question 
that sufficient sugar is present in this solution to form a yield as great as 
that I obtained with the untreated Pfeffer solution (1.024 g.). The treated 
Pfeffer solution contains all the components that A . niger requires for growth 
with the exception of sufficient iron and zinc. 
36. The efifect of increased acidity of the treated solution together with that of the addition 
of iron and of zinc. 
Strain W, 12. Treated Solution 
FeP04/Flask 
FeP04/Flask 
Yield 
Ph 
Sporulation 
0 mg. 
0.004 g- 
Fair 
I 
0.016 
3-4 
5 
0.004 
3-4 
20 
O.OIO 
3-4 
50 
0.021 
3-4 
100 
0.030 
3-4 
200 
0.065 
3-4 
Fe3(P04)2/Flask 
Fe3(P04)2/Flask 
Yield 
Ph 
Sporulation 
0 mg. 
O.OIO g. 
3-4 
Fair 
I 
0.032 
3-4 
5 
0.045 
3-4 
20 
0.094 
2-3 
Excellent 
50 
O.III 
2-3 
Good 
100 
0.147 
3-4 
200 
0.213 
3-4 
0.2 Cc. H3P04/Flask 
FePOi/Flask 
Yield 
Ph 
Sporulation 
0 mg. 
O.II7 g. 
2-3 
Excellent 
I 
0.123 
2-3 
5 
0.157 
2-3 
20 
0.154 
2-3 
50 
0.187 
2-3 
100 
0.277 
2-3 
200 
0.273 
1-2 
Fe3(P04)2/Flask 
Yield 
Ph 
Sporulation 
0 mg. 
0.071 g. 
2-3 
Excellent 
I 
0,106 
2-3 
. 5 
0.176 
2-3 
20 
0.170 
2-3 
50 
0.254 
2-3 
100 
0.437 
2-3 
200 
0.580 
2-3 
