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FUNGI IN CHEESE RIPENING. 83 
media to blue (alkaline) and maintain this character consist- 
ently. Many others when grown in blue gelatine (designating 
by dlue, gelatine 15 points acid to phenolphthalein—1o points 
alkaline to litmus on Fuller’s scale) begin by changing the 
blue to red. This change may vary from the faintest tinge of 
red in only that part of the medium directly in contact with 
the threads of the young colony to deep red over large areas. 
Oidium lactis and Roquefort Penicillium produce at times a very 
slight pink, which barely traces the outer limits of the young 
colonies before the blue reaction begins to appear. At other 
times the red if appearing at all has been so evanescent as to 
be overlooked. It has been suggested that this slight appear- 
ance of acidity might be due to the excretion of carbon dioxide 
in respiration, which although continuous, is afterward masked 
by many times larger changes in other substances. 
The Camembert Penicillium, and several of the very common 
green species of Penicillium, when grown upon blue gelatine, 
at first turn all the substratum in contact with the growing 
colonies to a bright red. Some species produce areas of red 
beyond the limits of the mycelium. These effects are most 
clearly seen by examining the colony from the under side. 
Later a spot of blue appears in the center of the colony below 
and gradually extends outward, until commonly the entire 
mass of culture medium has become blue. ‘This often involves 
a change of reaction in agar or gelatine two to three centimetres 
beyond the colony. It is thus clear that there must be either 
the secretion or the excretion by the mycelium into the medium 
of a substance capable of changing this reaction, or the absorp- 
tion from the medium of some substance, thus changing its 
reaction. ‘Ihe exact nature of this change has not been deter- 
mined. Increase in the percentage of acidity or of alkalinity 
retards the change of reaction. In certain experiments phenol- 
phthalein was introduced into red litmus media and several 
species of Penicillium and Oidium lactis were grown upon it. 
With the Camembert Penicillium the entire mass of agar be- 
came blue in a few days, remained so for nearly three weeks, 
then the characteristic pink color for the alkaline reaction of 
phenolphthalein appeared on the under side of the colony. This 
was tested by opening the colony with a platinum needle and 
introducing a very small drop of normal acid, when the pink 
