SECTION VI. 

 LACTIC FERMENTATION AND ALLIED DECOMPOSITIONS. 



CHAPTER XXI. 

 GENERAL CHARACTERISTICS. 



134. Discovery of the Lactic Acid Bacteria. 



IN chemical text-books acetic acid is generally characterised as being the first acid 

 known to man. This assumption cannot, however, be considered as probable, 

 since, in order to obtain acetic acid, the previous preparation of alcoholic liquids is 

 necessary, and the human race in its earliest stage of civilisation, viz., nomadic life, 

 would hardy have attained that skill the production of wine and vinegar, even 

 in the most primitive fashion, presupposing a settled mode of existence. On the 

 other hand, the flock-owning nomadic races must, at a very early period, have 

 noticed that the milk supplied by their animals very quickly underwent altera- 

 tion, and turned sour when left to itself. Lactic acid must therefore be regarded 

 as the earliest acid known to man, though not in a pure condition, since that 

 condition necessitates the employment of methods for removing all the other 

 constituents of the milk. This result was first accomplished by the Germano- 

 Swede Scheele in 1780. The earliest complete chemical investigation of the 

 souring of milk was instituted in 1833 by PELOUZE and GAY-LUSSAC (I.), 

 but from that date fully twenty-five years elapsed before the knowledge that 

 this process is a manifestation of vital activity on the part of sundry micro- 

 organisms assumed definite shape. It is true that already in 1701 Andry had 

 noticed that sour milk contained such organised microcosms. Nevertheless, this 

 observation remained at first as unproductive, as regards the comprehension of 

 the question, as did also the labours of sundry other subsequent workers. Among 

 these mention may be made of Blondeau, who in 1847 made a microscopic 

 examination of milk, and distinguished therein two types of micro-organisms : 

 the one (which he named Torula) was a yeast-like plant ; the other, a mould 

 fungus, which he assigned to Penicillium and held to be the cause of lactic 

 fermentation. 



We may recall to mind that Pasteur, in his treatise (against spontaneous 

 generation) in 1862, pointed to the non-success experienced by the opponents 

 of this theory, especially Schroder and Dusch, when they employed milk for 

 their refuting experiments. Knowing, as we do, that, before Pasteur, no one 

 had succeeded in rendering milk absolutely free from germs, it is therefore easy 

 to understand that up till then nothing definite could be urged against the hypo- 

 thesis, put forward by chemists, of the purely chemical nature of the process of 

 lactic fermentation. Thus, for example, ROWLANDSON (I.), under the influence 

 of the Liebig and Gay-Lussac theories of fermentation, denned the preliminary 

 conversion of lactose into lactic acid in the souring of milk as an oxidation pro- 

 cess, and expressed the nai've opinion that a cow that had been running about 

 (and therefore breathing rapidly) before milking would yield a milk rich in 



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