CHEMICAL STIMULATION OF GROWTH OF ASPERGILLUS NIGER 353 
PfefFer Nutrient 
Before 
At Time of 
Solution 
Inoculation 
Harvest 
• • • PH =3-4 
P^^ = 3-4 
+ O.I mg. Zn/L 

1-2 
+1.0 " 
3-4 
1-2 
+ lO.O " 
3-4 
1-2 
+ 0.2 CC. NH40H/flask 
< 6-8 
3-4 
+ 0.2 cc. H3P04/flask 
2-3 
2-3 
Additional evidence of the increased acidity attained through the growth 
of the organism and its relation to the zinc content of the cultures is given 
in experiment 25 (see above). See also experiment 6, etc. 
These acidity values though quite crude serve nevertheless to indicate 
clearly the existence of a parallelism between increase in growth, retardation 
of fructification, and increase in acidity of the medium. The maximum 
acidity attained is pH = 1-2 and corresponds (though see H3PO4 series) 
to maximum growth. "Stimulation" due to iron salts (ferric and ferrous 
phosphate and ferric sulphate) results in the same acidity. This value, it 
is to be seen, is in agreement with that of Clark and Lubs (10) — Ph = i-7» 
and that of Currie (11) — pn = 146. 
A few values obtained with the "Y" strain (experiment 26) are of 
essentially the same significance as those with the '*W" strain (experi- 
ment 25). 
26. The effect of an increase or of a decrease in acidity of the culture medium on the growth 
accelerations obtained by addition of zinc, 
Strain Y, 8 
Control 
Yield 
Ph on 
Harvest 
Fructification 
+ 0.2 cc. NH40H/flask 
+ 0.2 cc. H3P04/flask 
+ 0.2 cc. NH40H/flask + o.i mg. Zn/L 
" " " + i.o " " 
0.233 g. 
0.070 
0.420 
0.647 
0.651 
0.595 
2-3 
^3 
2-3 
^3 
2-3 
2-3 
Black with spores 
Retarded 
Sterile 
I append also an experiment (experiment 27) in which acid variation 
was estimated by titration. Ten cubic centimeters of each culture was 
titrated with sodium hydroxide in the presence of methyl orange. 
27. The effect of the addition of zinc to the culture medium on the rate of increase and the 
total acidities developed in the cultures. 
Strain W, 1 1 
Harvested 
Yields 
N/io 
NaOH 
No Zinc 
o.is Mg. Zn/L 
No Zinc 
0.15 Mg. Zn/L 
I day 
0.084 g- 
0.096 g. 
0 CC. 
0.53 CC. 
2 days 
O.II7 
0.297 
0.86 
2.80 
3 " 
0.088 
0.507 
2.45 
5-25 
4 " 
0.149 
0.670 
1.23 
5-95 
5 " 
0.230 
0.781 
2.10 
7.00 
7 " 
0.176 
0.910 
1-93 
7.88 
