62 
Pasteur and his Work, 
little greyish patches on the surface, which go on increasing 
progressively and rapidly. This is the Mycoderma grown from 
the seeds, or " germs " which the wine or vinegar accidentally 
contained, or which the air carried, — just as weeds grow in fields 
from seeds which are brought there by the wind or animals. That 
the latter may be also instrumental in extending the process of 
acetic fermentation is beyond doubt, for in vinegar manufac- 
tories, and in places where vegetable matter is souring, there 
are usually seen numbers of little reddish flies which come from 
we know not where, but which, by means of their feet or pro- 
bosces, convey the seeds of this cryptogam. 
When a bottle containing wine is subjected to a temperature 
of 120° to 140° Fahr., the wine remains sweet, because the 
Mycoderma germs in it, and in the air in the bottle, are killed by 
the heat ; but if the bottle be opened, the wine will sour, because 
new germs gain access. Wine in well-filled bottles, laid flat, 
does not become acid, because the Mycoderma cannot grow 
without a sufficient supply of oxygen ; for although air pene- 
trates the pores of the cork, yet it is in such minute quantity 
that the oxidisable constituents of the wine absorb it, without 
leaving any for the germs in the bottle. But when the bottles- 
are placed upright, the'corks become dry, and the air more readily 
passes through them ; so that the germs on the surface of the 
wine are surrounded by air, multiply, and break up the alcohol 
into acetic acid. 
The Orleans method of manufacturing vinegar, Pasteur deter- 
mined to improve, according to the discoveries he had made in 
acetic fermentation. The disadvantages attending the system 
hitherto were very serious, and have been briefly alluded to, 
Into large barrels is first introduced a quantity of good vinegar, 
with about a fiftieth part of wine. Eight days after, some wine is 
added, and in a week another quantity, until the barrel is half 
filled. Then vinegar is drawn off to a certain amount, and ffesh 
wine added to replace it, this process being repeated every 
eight days, the maximum quantity of vinegar obtained every 
week from one of these casks, or " mothers," as they are called, 
being a little more than two gallons ; but when the casks work 
badly, which is frequent, this quantity is diminished. It requires 
three or four months to prepare a " mother," which has to be very 
regularly fed with fresh wine, or all will be spoiled, and the busi- 
ness must be commenced anew ; the manufacture has to go on at 
all times, whether vinegar be required or not ; and the barrels 
cannot be stirred from their places during the process. 
Instead of the " mothers," Pasteur recommended vats placed 
in a chamber heated to about 76"' Fahr., and filled with vinegar 
and wine, on the surface of which the Mycoderma was sown, 
