208 Mr. W. K. Sullivan on the nature of Lactic Fermentation. 



According to the second view, fermentation is a vegetative 

 process, consisting in the growth of a plant at the expense of 

 the fermenting bodies. This view, which appears to have been 

 first suggested by Erxleben, was adopted by Caguiard de la Tour, 

 Schwann, Kiitzing, Quevenne, Dumas, Mitscherlich, and Mulder. 



There is this much in favour of the vegetative theory, that 

 yeast is undoubtedly the mycelium of a fungus or mould (a Peni- 

 cillium) in an abnormal condition. It consists of globules or 

 free floating cells, without a trace of rootlets, which are capable 

 of almost endless propagation, and which, from their submerged 

 position, are forced into a peculiar habit of development without 

 ever producing perfect fruit. 



Several observers, among others Hofmann and Berkeley, have 

 followed up the development of individual yeast-globules in fluid 

 surrounded in a closed cell with a ring of air, and have obtained 

 the true fruit proper to a Penicillium, and to one too which has 

 been more than once observed to grow on fermenting matter. 



It is also known that other species of mucor promote vinous 

 fermentation as well as the true yeast plant: a case is recorded of 

 the kind where a peculiar myceloid state of Mucor clavatus was 

 developed in raisin wine, the latter being, nevertheless, of pecu- 

 liar excellence*. 



But while there can now be no doubt that yeast is the myce- 

 lium of a fungus, there is still much room for difference of opi- 

 nion as to whether the plant be the primum movens of the 

 decomposition of the sugar, or only ancillary to it. 



Pasteur has recently instituted a series of ingenious experi- 

 ments, which have led him not only to adopt the plant theory, 

 but to extend it to all other kinds of fermentation. He says, 

 " That in the same manner as there exists in an alcoholic ferment, 

 beer yeast, which is found wherever there is sugar, which breaks 

 up into alcohol and carbonic acid, so there is a special ferment, 

 a lactic ferment, always present when sugar becomes lactic acid ; 

 and that if every plastic azotized matter may transform sugar 

 into that acid, it is because it is a suitable aliment for the deve- 

 lopment of that ferment." And further, " that there exist a great 

 number of distinct ferments, all having their speciality of actionf." 



He describes the lactic yeast to be formed of globules, or rather 

 threads somewhat swollen at the extremity, and about j^oth of a 

 millimetre in diameter, and to be organized like beer yeast. It 

 has long been known that carbonate of ammonia very much 

 favours fermentation ; but Pasteur has explained the reason, by 



* Mag. of Zool. and Bot. vol. ii. p. 340, quoted in Berkeley's ' Introduc- 

 tion to Cryptogamie Botany,' p. 295. 



I '. t Comptes Rendus de I'Academie des Sciences, vol. xlviii. No. 7 (February 

 1859), p. 337. 



