June 9, 1923 
Substrate and Hydrogen-Ion Concentration 
865 
on Irish-potato decoction from Ph 5.68 to 7.48. The hydrogen-ion 
concentration was increased from Ph 4.84 to 2.34 on Czapek’s solution. 
If a comparison is made of the hydrogen-ion change produced in the 
six vegetable decoctions, it will be seen that in some cases it is increased 
and in others decreased. This is contrary to what might be expected 
on theoretical grounds. Before these experiments were conducted it 
had been many times demonstrated that Rhizopus tritici made sweet- 
potato decoction more acid. For this reason it was predicted that it 
would produce similar changes when growing on other vegetable decoc¬ 
tions prepared in a similar manner. However, it was found that some 
of the decoctions (carrot, turnip, sweet potato) became more acid while 
others (string bean, Irish potato) became less so. 
The synthetic media were all more acid at the close than at the begin¬ 
ning of the experiment, Czapek’s nutrient solution showing a greater 
increase in hydrogen-ion concentration than either Pfeifer's or Richard's 
solutions. Beef bouillon, a solution not well suited to the growth of 
Rhizopus triticiy was very little changed in acidity, becoming less alkaline 
and more alkaline in experiments i and 2 respectively. 
The outstanding conclusion to be drawn from these experiments alone 
is that it is not safe to class any one fungus as an acid or an alkaline- 
producing organism. These experiments too clearly demonstrate that 
an organism may be an acid producer on one medium and the reverse 
on another. The class to which an organism belongs would clearly 
seem to depend upon the media used and should be determined in each 
individual case. 
ENZYM PRODUCTION 
The amount of enzym produced was measured by the time required 
to macerate raw sweet-potato and carrot disks i mm. thick suspended 
in the solution on which the fungus grew and in a water suspension of 
the mycelium. The time required to effect loss of cohesion of the cells 
of disks by the enzym secreted into the solution of the different media 
and retained by the mycelium is shown by Table II. It must be remem¬ 
bered that these results are only approximate, since it is not always 
easy to tell just when loss of coherence is complete. It is believed, 
however, that they are accurate within the limits of ± 5 per cent. 
Table II .—The time (in hours) required to macerate raw sweet-potato and carrot disks by 
the enzym in the solution and in a water suspension of the mycelium 
Media. 
Experiment i. 
Experiment 2. 
Solution 
(sweet 
potato). 
Hyphae. 
Solution. 
Hyphae 
(sweet 
potato). 
Sweet 
potato. 
Carrot. 
Sweet 
potato. 
Carrot. 
String-bean decoction- 
00. 
7, 0. 
7 to 24. 
4.5. 
7 to 24. 
7 to 24. 
7 to 24. 
7 to 24. 
5.0 
3-0 
6. 75 - 
None in 24. 
Do. 
Do. 
Do. 
None in 24, 
3-75 . 
2. 75 . 
2. 25. 
2-75 . 
None in 24. 
fin . . 
7 to 24. 
None in 24 
3.0. 
3.0. 
None in 24. 
6-5 . 
3.0. 
Irish-potato decoction- 
Carrot decoction. 
Turnip decoction. 
Sweet-potato decoction... 
Czapdc's solution... 
S-o. 
y|. C . 
7 to 24. 
7 to 24 
4 * 0.* . • • 
4‘0 . 
S- 5 . 
Consider¬ 
able in 30. 
do. 
5 . 
7 to 24. 
None in 30. 
...do. 
2.0. 
30. 
None in 24. 
2.0. 
s-s. 
None in 24. 
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