FUNGI IN CHEESE RIPENING. 87 
Comparative study of numerous cultures of many species of 
fungi upon gelatine gives, however, some very interesting sug- 
gestions. In many species which liquefy litmus gelatine 
rapidly, the area of liquefaction is surrounded by a blue (Alka- 
line) band. For example, in one experiment with Penicillium 
‘" 392,’ at its most active period of growtha colony fifteen milli- 
meters in diameter was surrounded by a liquefied area four to 
eight millimeters wide. This area was in turn surrounded by 
a band of intense blue shading gradually in a width of perhaps 
ten millimeters into unchanged red litmus-gelatine. The 
medium which had been liquified was almost colorless. Several 
suggestions may be drawn from many such observations. The 
change in acidity of the medium as has been noted above may 
be affected at*a distance of two to three centimeters from the 
colony. This change of litmus reaction advances faster than 
the area of liquefaction of the gelatine. The breadth of the 
area of liquefaction shows that the action of the fungus is nota 
digestion by contact, but the secretion into the medium, of dif- 
fusible digestive agents, z. e., enzymes. In most of these species 
liquefaction occurs only in areas having alkaline reaction. No 
general relation between acidity and digestion is established. 
The substantial uniformity of the results of repeated cultures 
of the same species of fungi upon gelatine made after the for- 
mula used, established its usefulness as a test of the ability of 
an organism to perform this particular digestion. It will be 
shown later that the ability to liquefy this variety of gelatine 
is not to be regarded as a general test of the ability of a species 
to produce active proteolytic enzymes. 
RAULIN’S FLUID. 
To test the ability of these species to grow in a medium en- 
tirely lacking in proteid, Raulin’s fluid was used as given by 
Smith and Swingle (B. P. I. Bulletin 55) but modified by leav- 
ing out the potassium silicate and zinc sulphate. Sterilized 
flasks of this solution were inoculated with Mucor, Oidium 
lactis, Camembert Penicillium and Roquefort Penicillium. All 
four grew. The Oidium lactis and Mucor did not appear to 
develop entirely normally. Both species of Penicillium grew 
richly and fruited normally. The culture of the Camembert 
mold, after growing several weeks, was examined chemically 
