FERMENTATION. 



C 318 ] 



FERMENTATION. 



of living organisms, are those which convert 

 saccharine infusions into spirit, vegetable 

 juices into beer, wine, &c., or vinegar j and 

 occur generally in watery solutions of vege- 

 table substances containing saccharine mat- 

 ters or other ternary compounds with a 

 certain amount of nitrogen ; with these is 

 included also the putrefactive fermentation 

 of moist animal or other highly nitrogenous 

 substances. 



Much obscurity still prevails upon this 

 subject; but all investigations appear to 

 tend in the direction of proving that these 

 changes are absolutely dependent upon the 

 agency of Fungi; and that each kind 

 of fermentation is produced by a distinct 

 vegetable organism. Thus: the vinous fer- 

 mentation appears to depend entirely upon 

 the growth of Yeast, a microscopic fungus, 

 in the liquid (see YEAST) ; while milk-fer- 

 inentation is caused by Bacterium lineola ; 

 butyric fermentation by Bacillus suUilis &c. 

 Yet, according to the experiments of Muntz 

 and Pasteur, it appears that the living cells 

 of the higher plants, can in the absence of 

 oxygen, act like fungi, and produce a true 

 introcellular alcoholic fermentation. The 

 Yeast-plant as ordinarily known, appears 

 so associated with Penicillium, that there 

 seems no doubt as to the necessary relation 

 between them. We find that beer, exposed 

 to the air at ordinary summer temperatures, 

 soon becomes coated with the minuter glo- 

 bules (conidia) of Yeast, forming a dry- 

 looking whitish powder over the surface ; 

 and very soon after, Penicillium glaucum 

 makes its appearance in fruit. Turpin found 

 the same thing in milk. Again, the ' vine- 

 gar-plant,' as it is called, which converts 

 solutions of sugar into vinegar, seems to be 

 undoubtedly the mycelium of Penicillium 

 glaucum, as it fructifies with the characters 

 of this when the liquid is exhausted ; but 

 the gelatinous mass of mycelium contains, 

 intermixed with the ordinary filaments of 

 this genus, spherical and elliptical cells and 

 chains of cells of all sizes, many of which 

 are undistinguishable from the Yeast- plant, 

 and the mycelium of Oidium. It must be 

 recollected also, that the growth of true 

 Yeast is favoured by a certain amount of 

 heat, while the Penicittium-ja.jceHu.in. grows 

 luxuriantly at ordinary temperatures. Dead 

 Yeast causes no fermentation. 



The f mother ' of vinegar, which finally 

 decomposes the acid, appears to be the same 

 plant ; and no satisfactory distinction can 

 be drawn between this and those mycelia 



forming cloudy flocks in and decomposing 

 various saline solutions, &c., described as 

 species of Hygrocrocis, Leptomitus, &c. The 

 decay of wood, again, is often greatly ac- 

 celerated by the growth of the mycelium 

 of Fungi, which seems to decompose the 

 organic compounds in the wood in the same 

 way that the Yeast does those in organic 

 liquids. A general law indeed appears to 

 prevail throughout the Fungi, that their 

 nutrition differs from that of all other plants 

 in depending exclusively on the absorption 

 and decomposition (with the evolution of 

 carbonic acid) of organic compounds, there- 

 fore consisting of the performance of the 

 operation of fermentation on the organic 

 matters upon which they feed. Details upon 

 the microscopic phenomena attending fer- 

 mentation produced by Fungi will be found 

 under YEAST, VINEGAR-PLANT, TORULA, 

 PENICILLIUM, and SCHIZOMYCETES. 



The fermentation of animal substances, 

 and of vegetable substances containing 

 abundance of nitrogen, in which ammonia 

 is liberated, is generally called putrefaction, 

 or the putrefactive fermentation. This pro- 

 cess has been shown to be produced by the 

 growth of living organisms resembling those 

 causing the fermentations alluded to in the 

 foregoing paragraphs ; and when the organic 

 liquids are thoroughly boiled and sterilized, 

 they may be kept indefinitely without 

 change. "These organisms appear in myriads 

 during the decomposition which takes place 

 when a piece of meat, &c., slices of potato, 

 fleshy Fungi, &c., are kept moist and ex- 

 posea to the air for some days in warm 

 weather; and they continue to multiply 

 until the putrefaction is complete, when 

 they die away. It is a question perhaps 

 whether they liberate the ammonia and 

 carbonic acid by a kind of respiration while 

 living, or as an excrement. 



One point of interest connected with the 

 fermentation -plants must not be passed 

 over, viz. that the supposed distinction be- 

 tween the chemical processes of nutrition 

 in animals and plants, falls to the ground 

 when these Fungi are taken into considera- 

 tion ; as they do not live by converting in- 

 organic substances into organic compounds, 

 but, like animals, decompose ready-formed 

 organic compoumds into others and into 

 their inorganic elements. 



BIBL. Turpin, Mem. Museum, 1840 ; Bail, 

 Flora, 1857, 417 ; Mulder, Chem. of Veg. 

 and An. Phys. ; Liebig, Lett. Chemistry, 

 1231; Gmelin, Organ. Chem.; Lowig, C'hem. 



