142 FERMENTATION I ACETOUS ; VISCOUS ; PUTRID. PRACTICE OF FERMENTATION. 
The fungus which causes the dreaded Acetic Fermentation is the My coderma Aceti. Its 
germs are so minute as to be only perceptible with a powerful microscope, when they are diffused in 
the liquor ; but when aided by exposure to air and a high temperature, they are quickly developed 
into chains and chaplets, that soon appear as a film of grey mould floating on the surface, and this 
is commonly called “ Flowers of Vinegar .” When this film has grown thicker, and becomes sub¬ 
merged, it takes on a gelatinous form of surprising toughness and lubricity, and is then called 
“ Mother of Vinegar f or the “ Vinegar Plant." The Mycoderma Aceti requires a warm tempera¬ 
ture, and a much more abundant supply of air than do the Saccharomyces which effect the Alcoholic 
Fermentation, and the more freely it is supplied the more rapidly the plant grows, and the more 
quickly is the vinegar produced. The Mycoderma Aceti has the power of decomposing sugar and 
alcohol singly or in combination, producing Acetic Acid and water without the evolution of Carbonic 
Acid gas. When the access of air is prevented, as should always be the first care of the Wine or 
Cider maker, its action is extremely slow. It is sure, nevertheless ; for the germs that find their 
way into closed vessels and well corked bottles will prevail in the long run. You may have an 
excellent bottle of wine or cider, but it will end in a bottle of vinegar, though it may take half a 
century to produce it. 
Viscous Fermentation, or “ Ropiness” is also caused by the rapid growth of the minute 
spherical germs of a fungus, not as yet specifically named. It quickly develops itself into chains of 
vesicles, and in this process changes the glucose into Gum and Mannite, with the evolution of 
Carbonic Acid gas. In some seasons Ropiness is very troublesome, and remedies in abundance have 
been recommended to check it, in accordance with the prevailing belief as to its cause. 
Putrid Fermentation, it need scarcely be said, is not due to the growth of fungus plants, 
but to the presence of Bacteria, Vibriones, and Infusoria in general, whose germs are also always 
present in the air, and when deposited under circumstances favourable to their growth develop 
themselves with great rapidity, to the destruction of the liquor. 
M. Pasteur, having thus proved that the vinous fermentation of saccharine fluids was caused 
by the plants growing from germ cells found on the surface of ripe fruits, next endeavoured to 
account for their presence. Infinitesimal as they are, and only perceptible by the aid of the 
microscope, he concluded that they formed part of the dust wafted about in the air. The germs 
themselves, and their mode of growth, he found to resemble the spores and habit of growth of 
certain funguses in the family group of Dcematiei , which are common on dead wood during the 
autumn months. Some species of this family, there is reason to believe, produce two forms of germs 
cells, the one set adapted to aerial growth, and the other capable of living when submerged in fluid 
by decomposing the substances with which they come in contact. Thus Alcoholic Fermentation may 
be briefly defined as “a chemical action resulting from the decomposition of glucose by the 
GROWTH OF CERTAIN CELLULAR FUNGUSES.” 
These results of M. Pasteur’s labours have met with general acceptance, and, so far as they 
have gone, they have completely changed the theories of fermentation formerly believed in. 
They require confirmation, however, and to be carried much farther, before the minute and 
complicated changes which are ever going on in the decomposition of organic substances—acting 
and re-acting on each other as they do—can be fully understood. It is happy for mankind that, 
