on Milk and Milk-Products. 
401 
These two instances of a close investigation are sufficient to 
show the variety of questions which have to be taken into 
consideration, and also the difficulty of carrying out researches 
of this nature. When speaking of the micro-organisms of 
butyric fermentation, we have mentioned that, under the influ- 
ence of this ferment, casein precipitated in the first instance is 
gradually dissolved again. As the butyric ferment never seems 
to be absent in cheese, there is full reason to assume that 
such ferment takes a prominent part in its ripening. We 
are also acquainted with ferments acting upon albuminoids so 
as to split them up into nitrogenous compounds of a less com- 
plex nature and alkaline reaction, ammonia being the sim- 
plest of the series. This kind of fermentation is also going on 
in cheese, for salts of ammonia never fail to be present in 
ripened cheese. That under certain circumstances which are 
not yet defined, there may be found amongst the products of 
decomposition of albuminoids bodies belonging to the class 
of ptomaines, i.e., compounds of a highly poisonous character, 
has been pointed out in a paper by the late Dr. Voelcker pub- 
lished in this 'Journal' (vol. xxiii. 1862), and more recently in 
America by Dr. Vaughan. Ptomaines are also considered 
products of an advanced decomposition (putrefaction) caused by 
micro-organisms. 
With the presence in cheese of larger organisms belonging to 
the vegetable kingdom, viz., moulds, we are much more familiar ; 
but it can scarcely be said that our knowledge of the way in 
which they act in the process of cheese-ripening is more 
thorough and complete than in the previous case. Roquefort 
is a cheese presumably made entirely from ewes' milk in a very 
limited district of France. This cheese contains, as is very well 
known, veins of green mould, and so much is it thought necessary 
that this mould should be present that the latter is specially 
prepared. It is grown upon bread made of wheat or barley 
and incorporated into the curd of which the cheese is formed. 
The growth of the mould is further encouraged by piercing the 
cheeses at regular intervals whilst they are kept to ripen, and 
thereby admitting air to the interior. The development of 
other organisms is at the same time kept back as much as pos- 
sible by storing the cheeses in cellars, or caves hewn out of the 
rock, the temperature being kept at from 40° to 50° Fahr. 
This temperature is unfavourable to the growth of the majority 
of micro-organisms, but does not interfere with the growth of 
the mould. Roquefort has a very characteristic flavour, as 
have Stilton and Gorgonzola, also cheeses which contain the 
green mould. How far the fermentations going on in these 
cheeses are similar or identical has not yet been ascertained. 
