FUNGI IN CHEHSE RIPENING. 75 
The further ripening of a Camembert cheese is attended by 
a gradual reduction of this acidity until the ripe cheese is 
usually alkaline to litmus. At the same time the mold action 
produces chemical changes in the mass of curd, which in from 
three to five weeks reduce the previously insoluble mass to a 
high percentage of solubility in water. In the latter stages of 
this ripening, compounds are formed which give the character- 
istic odors and flavors to this type of cheese. Associated with 
these chemical changes there is a progressive physical change 
from the firm curd to asoft buttery or even semi-liquid texture, 
characteristic of ripe cheese. The biological problems then 
were, in general, the determination of what organisms cause: 
1. ‘The changes in the acidity of the curd. 
2. The changes in the casein with the associated changes in 
the physical character of the cheese. 
3. The production of the flavors. 
4. ‘The recognition and control of deleterious species. 
CULTURE MEDIA AND METHODS. 
The common dairy fungi grow readily upon any of the 
staudard culture media. Among the media used have been 
peptone agar, whey gelatine, sugar gelatine with or without 
the addition of litmus, milk agar, gelatine and agar made with 
Raulin’s fluid, potato agar, potato plugs, and sterilized milk 
and curd. Special studies have involved other preparations. 
The fact that these fungi grow readily upon all of the common 
media has led to the selection of two preparations for constant 
use, and the careful study of all species found upon these. 
For this purpose the sugar gelatine described by Conn’ for the 
qualitative bacteriological analysis of milk, and potato agar 
have been used. 
The sugar-gelatine formula produces a type of carefully made 
and accurately titrated medium in which every effort is made 
to secure a uniform composition. Although absolute uniform- 
ity in chemical and physical properties is never obtained, the 
reactions of many species of fungi, when grown upon successive 
lots of gelatine made after this formula, have been so reliable 
as to commend its use for determining physiological characters. 
* Bacteria in Milk and its Products, p. 268. 
