148 PROCEEDINGS OF SECTION B. 
of cheese moulds are essential, and they are purposely added 
by means of mouldy bread, mats, or wires. In such cases 
the moulds undoubtedly play a part in giving a flavour to 
the finished cheese. These, however, have little to do in 
the ripening of the curd, and they play no part in the 
maturing of an ordinary Cheddar. The cause of the mpen- 
ing of firm cheese has for a long time been under discussion, 
but it is now understood that the gelatine-liquefying bac- 
teria have no influence, and that lactic bacteria, if they play 
a part at all, only regulate the process, possibly by starving 
out objectionable micro-organisms. The activa agents are 
two enzymes; one, galactase. occurs normally in milk; the 
other, pepsin, is added with the rennet. So far as we know 
at present, these are the only agents that cause the ripening 
of cheese. 
The Rancidity of Butter. 
The rancidity of butter has been ascribed to the action of 
bacteria, light, or air; and the most recent research, like all 
previous ones, does not furnish an answer to the question. 
The rancidity is not proportional to the free acid, but is 
proportional to the casein and milk-sugar, while light and 
air are without influence. The last finding is scarcely what 
one would have expected.* 
An Effervescng Milk Beverage. 
Kephir and koumiss are two effervescing milk beverages 
of Eastern Europe. Koumiss, originally made from mare’s 
milk by the Tartars, is now made in Western Europe by 
adding a little sugar and common yeast to cow’s milk. The 
casein becomes partly digested during the fermentation, and 
on this account the beverage has been recommended for 
invalids. 
The Retting of Flac. 
We now come to certain industries that utilise a mixed | 
fermentation of albuminoids and carbohydrates for the pur- 
pose of separating non-fermentable fibres and starch from 
other fermentable vegetable substances. 
The “retting’”’ of flax (hemp, loofa, &c.) has until quite 
recently been left to chance. The stalks of the harvested 
* Still more recent are the investigations of O. Jensen, who 
found that, when exposed to light and air, in the absence of micro- 
organisms, butter acquires an unpleasant taste and odour, but 
does not become rancid. Rancidity is only produced in the 
presence of bacteria and moulds. These require air for their 
development, and thus the rancidity proceeds from the outside to 
within the mass of butter. [Added 7.11.92.] 
