FERMENTATION. 



[ 258 ] 



FERMENTATION. 



entire conical fertile receptacle. The dicho- 

 tomously divided frond is of a yellowish 

 green colour. This genus is remarkable for 

 the mode in which the pedicel of the spo- 

 range becomes detached from the base of the 

 epigone before the former bursts (fig. 224) j 

 the perigone holds the sporange firmly be- 

 tween its valves until empty, and then lets 

 it fall out, together with its pedicel. Hence 

 fully-developed sporanges are seldomfound in 

 ihied specimens. (See Marchantie^.) 



BiBL. Hooker, Brit. Flora, v. pt. 1 . p. 107; 

 Bischoff, Nova Acta Jcad. N. C. xvii. 9/0. 

 pi. 68, English Botany, pi. 504. 



FERMENTATION.— The definition given 

 by Mulder is, — a chemical action efi^ected by 

 certain substances and transfeiTcd to others; 

 the primary substances being at the same 

 time decomposed, though they do not com- 

 municate any of their elements to the new 

 products. Under this name are understood 

 various processes of decomposition of organic 

 compounds, although it would be desirable 

 to restrict it to those taking place with the 

 cooperation of living organisms. The most 

 familiar examples of the fermentation pro- 

 duced by the growth of living organisms, are 

 those which convert saccharine infusions into 

 spirit, vegetable juices into beer, wine, &c., 

 or vinegar, and occurring generally in watery 

 solutions of vegetable substances containing 

 saccharine matters or other ternary com- 

 pounds with a certain amount of nitrogen ; 

 with these is included also the putrefactive 

 fermentation of moist animal or other highly 

 nitrogenous substances. 



The vinous fermentation appears to de- 

 pend entirely upon the growth of Yeast, a 

 microscopic fungus, in the liquid (seeYE a st); 

 and the same plant is not only capable of pro- 

 ducing the conversion of spirit into vinegar, 

 but will also give rise to the peculiar fer- 

 mentations of milk, tannic acid, &c. Much 

 obscurity yet prevails upon this subject, but 

 all investigations appear to tend in the direc- 

 tion of proving that these changes are abso- 

 lutely dependent upon the agency of Fungi. 

 The natiu'e and characters of the fungoid 

 productions are themselves but imperfectly 

 understood, for the same species seems to 

 present very dififerent forms under different 

 conditions of temperature and in different 

 liquids, while it is very possible that the 

 same changes may be ])roduced in any given 

 liquid by the growth of the mycelium of dif- 

 ferent kinds of Fungi. The Yeast-plant, as 

 ordinarily knovsni, appears so often associated 

 with Penicillium, that it is impossible not to 



suspect some relation between them. We 

 find that beer, exposed to the air at ordinary 

 summer temperatures, soon becomes coated 

 with the minuter globules (spores) 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 'vinegar-plant,' as it is called, which 

 converts solutions of sugar into vinegar, 

 seems to be undoubtedly the mycelium of 

 Penicillium glaucum, as it fruits with the 

 characters of this when the liquid is ex- 

 hausted; but the gelatinous mass of myce- 

 lium contains, intermixed with the ordinary 

 filaments of this genus, spherical and ellip- 

 tical cells and chains of cells of all sizes, 

 many of which are undistinguishable from 

 the Yeast-plant, and the mycelium oiOidium. 

 It must be recollected also, that the growth 

 of true Yeast is favoured by a certain amount 

 of heat, while the Pewici/Zmm-mycelium 

 grows luxuriantly at ordinary temperatures. 



The '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 form- 

 ing cloudy flocks in and decomposing various 

 saline solutions, &c., described as species of 

 Hygrocrocis, Leptomitus, &c. The decay 

 of w^ood, again, is often greatly accelerated 

 by the growth of the mycelium of Fungi, 

 which seems to decompose the organic com- 

 pounds in the wood in the same way that 

 the Yeast does those in organic liquids. A 

 general law indeed appears to prevail through- 

 out the Fungi, that their nutrition differs 

 from that of all other plants in depending 

 exclusively on the absoi'ption and decompo- 

 sition (with the evolution of carbonic acid) 

 of organic compounds, therefore consisting 

 of the performance of the operation of fer- 

 mentation on the organic matters upon which 

 they feed. Details upon the microscopic 

 phsenomena attending fermentation produced 

 by Fungi will be found under Yeast, Vine- 

 gar-plant, ToRULA and Penicillium, 

 and Parasitic Fungi. 



The fermentation of animal substances, 

 and of vegetable substances containing abun- 

 dance of nitrogen, in which ammonia is libe- 

 rated, is generally called putrefaction, or the 

 j)utrefr active fermentation. This process 

 appears to be accompanied or produced by 

 the growth of living organisms differing from 

 those causing the fermentations alluded to in 

 the foregoing paragraphs. These are the 

 extremely minute creatures called Vihriones, 



