CHEMICAL STIMULATION OF GROWTH OF ASPERGILLUS NIGER 359 
in the proportions and concentrations of the Pfeffer nutrient solution which 
probably occur are not factors of primary significance. 
With a culture medium so treated I have obtained on addition of both 
iron and zinc a dry weight of 1.158 g., and with the untreated Pfeffer 
solution a yield of 1.024 g. Both these values are maximum values for the 
W strain when supplied with iron and zinc. The maximum yield I have at 
any time obtained is 1.174 g. in culture with my original strain grown on 
Pfeffer solution and in Jena glass. 
32. The effect of treatment of the magnesium sulphate as shown by its action on growth. 
Strain W, 7 
(A) ic 
) : 5 : 130 
(B) 10:5: 130 (MgS04- 7H2O Purified). 
No Zinc 
i.o Mg. Zn/L 
No Zinc 
1.0 i\Ig. Zn/L 
0.718 g. 
0.757 g- 
0431 g- 
0.785 g- 
0.776 
0.768 
0.432 
0.849 
0.772 
0.752 
0.456 
0.839 
0.668 
0.836 
0.472 
0.839 
0.725 
0.882 
0.491 
0.923 
0.732 
0.799 
0.456 
0.847 
Solution (B) was prepared with MgS04.7H20 that had been autoclaved in 26% 
solution with 30 g. CaCOs per liter, the solution after treatment being decanted and used 
In making up the Pfeffer solution. The "no zinc" under solution (B) refers to the fact that 
none was added to the magnesium sulphate before its treatment; " + 1,0 mg. Zn/L" refers 
to the fact that enough zinc was added to the magnesium sulphate before treatment so 
that in the preparation of the Pfeffer solution this concentration of zinc should result. 
That is, the 26 percent solution of MgS04.7H20 contained in the latter instance 2.0 mg. 
Zn/L before treatment with CaCOs. The zinc cultures were sterile; excess zinc, p of 
II cultures on harvest was 1-2. 
The results of experiment 32 indicate clearly that the treatment with 
CaCOs acts essentially through a reduction of the zinc content of the 
MgS04.7H20. With solution (A), zinc is present in too high concentration; 
in solution (B), the treatment has apparently removed an appreciable 
amount of zinc, as is evidenced by the increased yield and increased fructi- 
fication. As respects solutions (A) and (B) in those cases in which no zinc 
was added, we note that the treatment results in a reduction in yield. On 
the other hand, a comparison of the cultures in solution (B) with and with- 
out zinc would indicate that the action of the CaCOs cannot consist in any 
action on the MgS04.7H20, but must depend on the removal of the im- 
purities present. 
After decantation of the solution from the CaCOs, the residue (15 g. 
CaCOs + 100 cc. Pfeffer solution) was used as a medium. An excellent 
"stimulated" culture resulted, a demonstration that the "stimulative" 
substances (zinc) had been removed from the Pfeffer solution by the CaCOs. 
The cultures in the treated solution exhibited much scantier growth and 
