STEINBERG: GROWTH OF ASPERGILLUS NIGER 13 
the culture sufficient zinc (or other substances having a similar 
action) to influence the growth of the organism, even if zinc is 
not one of the ingredients entering into the formula for the 
manufacture of pyrex. On this assumption the decrease in the 
effect as the cultures are continued generation after generation 
could be laid to a leaching out of the element from the surface 
layers of the glassware. That the decrease would not be a steady 
one is to be expected from the well-known complexity of the solu- 
tion processes taking place when glass is in contact with liquids. 
In addition it is to be assumed that there may be other uncon- 
trolled sources of minute amounts of zinc, such as dust, etc. 
The differences in the behavior of the W and Y strains, as the ex- 
periments progressed, can be quite satisfactorily accounted for on 
the basis of the greater sensitiveness of the latter to the presence 
of zinc. 
It is, therefore, quite probable that the differences existing in 
the literature between the results recorded by different investi- 
gators can, in part at least, be attributed to the use of strains hav- 
ing different zinc optima. While furthermore, possibly, the pres- 
ence to varying degrees of unrecognized traces of zinc in the 
medium may have been an additional factor in producing these 
differences. 
In conclusion, through the courtesy of Dr. Charles Thom, I 
am able to include a description of these strains based on his 
examination of cultures W5 and Y5. 
“In both cultures the primary sterigmata measure 20 to 25 
microns long by 3 to 6 microns in width. The secondary sterig- 
mata are nearly uniform throughout the group and hence may be 
disregarded. The conidia are black when ripe, varying in both 
cultures considerably in diameter with an average of about 34 
to 4 microns, sometimes 5 microns. They are smooth at first, 
later more or less rough. The roughnesses in strain Y are some- 
what less prominent than in strain W. These differences are 
differences in quantity only. The nature of the reaction is the 
same in each. These stalks of strain Y run 1,800 to 2,000 mi- 
crons. In strain W they are about 700 microns long. They 
would therefore, fall respectively into section 2 and section 1 of 
Aspergillus niger as discussed by Thom and Currie, page 6” (7). 
CoLuMBIA UNIVERSITY 
