256 
WILLIAM J. ROBBINS 
medium lacking potassium on the activity of the diastase. Deter- 
minations of the digestion of starch by Taka diastase in this medium 
show a very marked retardation apparently due to the concentrations 
of Ca(H2P04)2 and MgS04 present. 
That the results in Table VIII do not necessarily indicate a con- 
nection between potassium and diastase secretion is also shown by 
the following experiment. 
The time for digestion of a given quantity of starch in Czapek's 
medium,^ with the carbon supplied as .4 percent of soluble starch and 
in media in which each of the elements generally accepted as essential 
for the fungi was replaced by some other element, was determined. 
The substitutions made were as follows: 
Minus nitrogen, NaNOs, replaced by NaCl 
" potassium, K2HPO4, " " CaHP04 
KCl, " " Ca(N03)2 
" phosphorus, K2HPO4, " " K2SO4 
" magnesium, MgS04, " " K2SO4 
" sulphur, MgS04, " " MgCU 
FeS04, " FeCl2 
" iron, FeS04, " " NaCl 
Penicillium camembertii, Aspergillus OryzcB (Alhbury) Cohn, 
Mucor Rouxii (Calm) Wehmer, and a species of Fusarium of the 
subulatum type, were used to inoculate these cultures. They were 
grown at room temperature and tested daily for starch by the method 
of Katz. As the culture medium showed complete disappearance of 
the starch the dry weight of the mycelium was determined. 
It would appear from the data as summarized in Table X, which 
represent the averages of triplicate cultures, that nitrogen is the 
only element whose absence makes any considerable difference in the 
time required for digestion. 
It is also noteworthy that these four fungi may be separated into 
two groups: the Fusarium sp. and Mucor Rouxii, which digest starch 
^ The composition of this medium is 
NaNOs 2 g. 
K2HPO4 I g. 
MgS04 05 g. 
FeS04 001 g. 
KCl 05 g. 
Water 100 cc. 
