June 9,1923 
Substrate and Hydrogen-Ion Concentration 
875 
material as the hydrogen-ion concentration decreased, with one excep¬ 
tion. In the solution with an original Ph of 8.86, which is apparently 
too alkaline for normal growth, the dry weight was somewhat less than 
it was in the solution with a Ph of 8.21 (Table VI). 
It has been intimated that the maceration which takes place in solu¬ 
tions after they have been steamed is due to the action of some one or 
more acids produced in the solution by the fungus. A number of acids 
have been shown by different investigators to be formed by fungi in 
nutrient solutions, among them being oxalic, acetic, and formic. These 
three organic acids, together with hydrochloric acid and sodium hydroxide 
were made up to different hydrogen-ion concentrations and their ability 
to dissolve the middle lamellae determined. The results showed that 
maceration could be brought about by the acids in high hydrogen-ion 
concentrations and by the alkali at a Ph of about 12 or above. Oxalic 
acid at a Ph of 2.13 macerated raw sweet-potato disks in from ?4 to 48 
hours at a Ph of 2.44 in 72 hours. No maceration occurred in 72 hours 
by this acid at a Ph of 2.76. Acetic acid appeared to require more time 
to complete maceration than oxalic acid at the same concentration. 
Acetic acid of Ph 2.13 macerated the disks in 72 hours, while at Ph 2.40 
the amount of maceration was very slight in that length of time and was 
entirely absent at a Ph of 2.44. In a Ph 1.99 of formic acid maceration 
was nearly complete in 6 hours, at Ph 2.16 in 24 hours, and at Ph 2.23 
in 54 hours. At hydrogen-ion concentrations of Ph 2.40 and 2.57, there 
was slight and no maceration, respectively, in 54 hours by this acid. In 
full strength formic acid maceration was complete in 3 hours. Hydro¬ 
chloric acid of a Ph 2 will induce slow maceration. A comparison of 
these results with those obtained when Czapek's solution was used shows 
that the loss of coherence of the cells of sweet potato disks occurs in pure 
solutions of these acids at about the same hydrogen-ion concentration 
as in Czapek’s solution and in about the same length of time. Oxalic 
acid macerates a little more rapidly than acetic acid at the same con¬ 
centration, and formic acid a little more rapidly than either oxalic or 
acetic. 
The results of these investigations seem to indicate that no pectinase 
is produced in Czapek's nutrient solution when glucose is used as a 
source of carbon. However, an acid is produced in sufficient hydrogen- 
ion concentration to cause a dissolution of the middle lamellae identical 
with that caused by pectinase. It was found also that the original Ph 
value of the solution had no influence on the secretion of pectinase. 
In all concentrations of Czapek’s solution in which the fungus grew the 
hydrogen-ion concentration was increased, the greatest increase being 
in the solutions with the highest Ph values. 
A middle lamellae splitting enzym was produced when pectin alone 
was used as a source of carbon in Czapek’s nutrient solution and to^a 
less extent when combined with glucose. It had been suspected that 
the failure to obtain maceration in Czapek’s solution was not due to the 
absence of the enzym, but to its inactivation by the acid formed. 
Brown {2) showed that the addition of some of the organic and mineral 
acids to extracts of Botrytis mycelium retarded the action of the enzym, 
the time required to macerate potato disks being increased with the 
increase in the concentration of the acid. A point was finally reached 
when inactivation was complete. The retarding action of all the acids, 
was found to be about the same up to a certain concentration beyond 
