360 
ROBERT AARON STEINBERG 
Spore formation than the control. The conidiophores in the former had 
apparently been reduced to a minimum length. 
33. On the removal of added zinc from the culture medium by treatment with CaCOs. 
Strain W, 7 
Control 
1 
0 Mg. Zn/L + 30 g. CaCOs/L 
CaCOs^Added Before Sterilization 
CaCoj Added After 
Sterilization 
CaCOs Not Removed 
Decanted Solution 
0.078 g. 
0.545 g. 
0.039 g- 
0.759 g- 
0.082 
0.581 
0.050 
0.993 
0.091 
0.802 
0.042 
0.750 
0.087 
0.780 
0.043 
0.476 
0.090 
0.558 
0.039 
0.952 
0.086 
0.653 
0.043 
0.786 
Cultures prepared from 
solution decanted from CaCO; 
HNO3 
0.1 cc. /flask 0.084 g. 
0.1 0.103 
0.2 No growth 
0.2 " " 
As can be seen from experiment 33, the evidence for the removal of zinc 
by this method of treatment with CaCOs is quite conclusive. Furthermore, 
it is to be noted that the addition of CaCOs to a zinc culture (i mg. Zn/L) 
depresses the yield least when added after sterilization, to a greater extent 
when added before sterilization, and most when it is added before steriliza- 
tion and the supernatant liquid is removed by decantation. That is, the 
presence of calcium carbonate in the cultures causes a decrease in the rate 
of growth similar to that described by Wehmer (68), Butkewitsch (8), and 
Nikitinsky (48). If the calcium carbonate is added before sterilization, 
the effect of the heating in the sterilization process will be to cause the 
hydrolysis and precipitation of the zinc. The constituents of this residue 
go slowly into solution, thus affording zinc and iron necessary for the 
increased growth. If, however, the residue of calcium carbonate with its 
contained zinc, etc., is removed, as is the case when the solution is decanted, 
then growth is sharply limited. Indeed, in the latter case it is less than in 
the untreated Pfeffer solution. 
I next tested whether the addition of nitric acid to the treated solution 
influences the yield. Two duplicates with o.i and 0.2 cc. HNO3 per flask 
respectively were inoculated. In the latter no growth occurred, as was 
the case with the Pfeffer solution without treatment (experiments 20 and 
23). With 0.1 cc. HNO3 per flask, the growth was sHghtly accelerated, 
and, as was found to be the case with the untreated Pfeffer solution, the 
