FERMENTATION. 507 



dioxide, the process also giving rise to a small quantity o£ succinic acid aud 

 glycerine. This fermentation is never very noticeable in living plants in free 

 nature; there it is at any rate only cai-ried on to a small extent. It is very 

 important in the extensive artificial production of alcoholic beverages, for example, 

 of wine, cider, beer, brandj', " pulque ", rum, and many more, from grapes and other 

 fruit, and from grape-sugar, obtained from starchy seeds, tubers, and roots. 



Moulds consist of colourless, elongated, thin-walled cells, which appear to the 

 naked eye like extremely delicate threads. These divide up by the intercalation 

 of transverse walls, but they do not separate into their individual elements like 

 the bacteria. The threads multiply very rapidly, and frequently numerous threads 

 are crossed and intertwined like the threads of a cobweb, forming a loose, white 

 net-work. They generally dwell on damp or fluid substrata, and closely invest 

 them with their crowded threads. They also penetrate into the interior of these 

 substrata. The cells which make their way into sugary solutions assume another 

 form; they remain short, and increase by sprouting. The bud-forms of the mould 

 are often so like Yeast that they are mistaken for it. Only the parts of a mould 

 which respire and are in contact with the oxygen of the air develop spores, these 

 being usually distributed by currents of air; the parts submerged in a fluid to 

 which the free oxygen of the air has no access do not form spores, but they 

 multiply with incredible rapidity, just like Yeast and bacteria. This multiplication 

 is carried on at the expense of the organic compounds contained in the liquids or 

 succulent bodies attacked by the mould. The changes in the objects attacked 

 are not limited to the acquirement by the mould of as many organic compounds 

 as it requires for food, but the whole mass becomes decomposed and destroyed, 

 and finally is wholly converted into carbon dioxide, water, sulphuretted hydrogen, 

 ammonia, and other volatile substances — a process which has already been 

 describeil. This decomposition brought about in the absence of oxygen must be 

 termed fermentation. If the fluids and succulent bodies attacked by the moulds 

 contain nitrogenous compounds, they make their presence known by the unpleasant 

 odour they give ofl" when undergoing fermentation, i.e. putrefaction. If, on the 

 other hand, non-niti-ogenous compounds are fermented by a mould, alcohol may 

 be produced. In sweet, fresh fruit which has been attacked by moulds, the cells 

 of the mould which permeate the succulent tissue produce a fermentation of the 

 juices by which alcohol and ethereal oils first arise as products of decomposition, 

 and by which the characteristic smell of putrescent fruit is produced. It is 

 ascertained that one species of mould, Aspergillus niger, when on the surface 

 of a tannin solution, consumes the tannin in the presence of atmospheric air, by 

 which means carlion dioxide is formed. When this same species is submerged 

 in the fluid, and has no free oxygen at disposal, it splits up the tannin completely 

 into glucose and gallic acid. It has also been shown that mould cells which get 

 into the blood of living men and animals cause it to decompose as do bacteria, 

 i.e. they produce severe diseases, sometimes ending in death. Many species of 

 mould not only bear the high temperature of the blood without injury, but 



