June 9, 1923 
Substrate and Hydrogen-Ion Concentration 
867 
of carbon, but was likewise produced when other carbohydrates were 
employed. The substances most closely allied to inulin were most effi¬ 
cient in the production of the enzym. Investigations along similar lines 
have been made by Went {22), Wortmann {24), Dox (5), Pfeffer (79), 
Brunton and MacFayden (3), Harter (8 ), and others. Went, for instance, 
showed that Monilia sitophila secreted a number of enzyms, some of 
which w^ere produced only when the particular substances on which they 
act were present in the culture solution. Brunton and MacFayden found 
that a bacterium formed diastase when cultivated on starch paste but 
not when grown on meat broth. Dox, on the other hand, demonstrated 
that the enzyms were secreted by Penicillium camemberii, regardless 
of the chemical nature of the substrate. He found that by cultivating 
the fungus on any particular substratum the quantity of the correspond¬ 
ing enzym could be increased, but that no enzym not normally produced 
by the organism could be developed by any special method of nutrition. 
Harter likewise showed that when different carbohydrates were used 
alone or in combination in the culture medium, although amylase was 
produced when sugars alone were employed, it was secreted in greatest 
abundance when starch was the only source of energy. 
The preceding review of some of the literature shows that the quantita¬ 
tive regulation of enzyms is a rather common phenomenon. The quali¬ 
tative regulation, however, has been demonstrated in only a few cases. 
Failure to demonstrate the presence of an enzym does not necessarily 
constitute positive proof that it is not secreted. It is a well known fact 
that some enzyms act only under certain conditions—that is, in the 
presence of certain acids or alkalies or electrolytes or other substances, 
the so-called co-enzyms. For example, it has been shown that the 
presence of either the chlorin or bromin ion is absolutely essential to 
the activity of pancreatic amylase (7). It is a fact, however, that the 
writers have been unable to demonstrate the production of pectinase by 
R. tritici on Czapek’s, Pfeffer’s, and Richard’s solutions and on beef 
bouillon. On the other hand, it was freely produced in all vegetable 
decoctions with the exception of prune decoction, where its secretion was 
doubtful. 
With these facts in mind the writers suspected that there might be 
some substance or substances in the vegetable decoctions which were 
stimulating the production of pectinase that were absent in the synthetic 
media and in beef bouillon and that this substance was probably one or 
more of the pectic compounds. Experiments were therefore initiated in 
which pectin obtained in as pure a state as it was possible to make it was 
introduced alone and in combination with glucose into Czapek’s modified 
nutrient solution as the available sources of carbon. 
The pectin was obtained from the carrot, the method described by 
Hunt (70) being followed for the most part in its preparation. A num¬ 
ber of flasks were prepared, using Czapek’s modified nutrient solution as 
the substrate. In some cases dextrose (20 per cent), in others pectin 
(i per cent), and in still others dextrose (20 per cent), and pectin (i per 
cent) in combination were supplied as the source of carbon. Thirty 
cubic centimeters of these solutions were placed in each flask and after 
inoculation with a spore suspension of Rhizopus tritici the cultures were 
incubated at 35° C. At the end of 4 days’ growth the mycelial felts 
from all of the flasks of a single series were combined into one compound 
sample and prepared according to the usual method with acetone and 
ether for macerating experiments. Likewise, the solutions on which the 
