8 STEINBERG: GROWTH OF ASPERGILLUS NIGER 



Weeks si isolation | Number of transfers Ww ¥ ‘ 
I Original | 0.237 gram 0.546 gram 
3 I On aa 3.486." 
5 2 0.217 0,302 = 
8 3 | O1I9. O.545 
9 - 6.105. O308 
rae) 3 O:530): C270 G5 
19 5 05354" O.4400-°: 
20 6 O,1g0- — 
22 6 | — 0:205.° 7" 
23 7 O:520 20. — 
24 7 0.086 “* 
25 pole | Osho st 8.41862 
26 8 | Oras." 
27 8 Gage: o: — 
28 9 Oxs7 0.232 
29 10 @:08s C4708 
30 Io or30 Ors 
31 Io ap) ty a ae C272 




become more evident, in spite of the confusing experimental vari- 
ations, on reference to the effect of constant amounts of zinc on- 
the growth at different periods of time. Summarizing the yields 
obtained for the entire period with concentrations of 0.01 and 
0.10 mg. Zn/L we find: 






Weeks since pooner of oon mg. nil. | oro mg. Ene 
isolation ransfers w | y | w Y 
I Origi | | 0.903 g o.81I g 
3 Ai 0.565 g. | 0.781 g — os 
5 2 | fe a By say 0.805 ‘* 
8 3 _ 0.635": 
° 6 0.287 “ —_ 0.851 “ 
2 6 _ 0283."° — 0.823" 
30 10 0.198 “* 0.268 *‘ _— oa 
31 10 0.287 “ 0.440 “ ooeo © | O70." 

The results obtained in ‘‘zinc-free”” media and with media con- 
taining 0.01 mg. Zn/L are shown graphically in TEXT FIG. 4. 
There is, it will be seen, a perceptible decrease in the yields 
obtained with both strains with time. While experimental 
variations due to at present unascertained conditions tend to 
obscure this phenomenon, a survey of the yields for identical 
zinc concentrations cannot but make evident that the capacity 
for growth of the organisms in the presence of small amounts 
of zinc has decreased. Not only the apparently zinc-free but 
also the zinc cultures exhibit the same result. Whereas strain 
