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276 Structural and Physiological Botany. 
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Fungus-spores ; and may, under these conditions, remain 
fresh even for some years. As soon, however, as access of 
these organisms is rendered possible, a rapid and active | 
decomposition immediately sets in. With free access of air, 
decay, z.¢. an active oxidation, takes place, the products 
being water, carbon dioxide, and simpler organic compounds. - 
When the access of air is less complete the mode of decom- 
position is different, and less. simple substances, usually of 
an offensive odour, are formed under the influence of Bac- 
terla ; and the process is called putrefaction. Another set 
of processes of decomposition allied. to these are called by 
the special name of Fermentation ; such are the formation of 
alcohol from saccharine solutions, as also the lactic, butyric, 
acetic, and mucilaginous fermentations. The greater part 
of the substance infested by the organisms which incite fer- 
mentation breaks up in the process into simpler compounds, 
the organisms themselves taking up only comparatively 
very small quantities. of nutriment. When the organisms. 
which cause decomposition find the oxygen needful for their 
growth free, they absorb it eagerly, and multply rapidly ; 
but when, on the other hand, they have no access to free 
oxygen, they withdraw it from its combinations ; and this 
gives an impetus to further decomposition. If, for example, 
‘mother of vinegar,’ AZycoderma acet?, the cause of acetic 
fermentation, 1s grown on the surface of an alcoholic fluid 
adapted for its nourishment, the alcohol is converted into 
acetic acid during the multiplication of the Mycoderma ; 
and it has been discovered that this process is dependent | 
on the absorption of oxygen by the Fungus out of the at- 
mosphere, and its transmission to the alcohol. When the 
growth of the Fungus has once been induced, the JZyco- 
derma continues to convert fresh portions of the alcohol 
into acetic acid. Hence, because all acetic fermentation 1s 
accompanied or caused by the propagation of the JZyco- 
derma acett, the manufacture of vinegar may be improved by 
its cultivation in a scientific manner. When the A/ycoderma 
