20 THEORIES OF FERMENTATION 



solutions of organic substances such, for example, as are stored for use as 

 nutrient media for bacteria also gradually undergo slight modifications when 

 air and light find admittance thereto. The proof that these changes are of a 

 purely chemical nature lies in the fact that they do not occur when the causes 

 indicated are absent. 



In many instances the oxidation of the medium effected in this manner exerts 

 a favourable influence on the development of the organism subsequently inoculated 

 therein. Such, for example, is the case with beer-yeast. In wort through which 

 air has been blown ("roused ") for some time, the yeast sown therein develops 

 more rapidly, and deposits more quickly and satisfactorily (" breaks " better) at 

 the conclusion of fermentation, a circumstance highly desired by the brewer. 

 Sunlight possesses an even greater decomposing power than that of atmo- 

 spheric oxygen. On this point we are indebted to E. DUCLAUX (I.) and W. 

 SEEKAMP (I.) for exhaustive researches, the former of whom found that, in 

 presence of air, a sterile solution of tartaric acid is split up by sunlight into 

 formic acid, carbon dioxide, and water, according to the equation 



C 4 H 6 6 + 30 = 2CH 2 2 + 2 C0 2 + H 2 0. 



In a second communication (II.) on this subject the same worker showed that 

 glucose and lactose in a sterile alkaline solution gradually decompose into alcohol 

 and carbon dioxide on exposure to sunlight, even when oxygen is excluded. The 

 same products are yielded by them when fermented with yeast. When baryta 

 (BaH 2 2 ) or lime (CaH 2 O 2 ) was substituted for the alkali, lactic acid was produced 

 instead of alcohol. Under the same treatment maltose yields dextro-lactic acid ; 

 levulose, levo-lactic acid ; and invert sugar the optically inactive acid. A similar 

 observation was made by WEHMEE (I.) with respect to a sterile solution of oxalic 

 acid. 



These observations are of great interest to the bacteriologist, from a theo- 

 retical as well as a practical point of view, as they convey a special warning to 

 protect his stores of nutrient media from the influence of sunlight. G. Roux, as 

 the result of his adverse experiences, had already given the same warning as to 

 the prejudicial influence of the changes produced by sunlight on bacterial growth, 

 prior to the more exhaustive research by Duclaux. 



These facts have a further interest, more nearly connected with our definition 

 of fermentation, since they demonstrate the occurrence of decomposition processes 

 by purely chemical means, apart from the intervention of micro-organisms. We 

 will therefore modify our general definition of fermentation, and, in place of 

 stating that fermentation is a process accomplishing transformations of matter 

 with the aid of micro-organisms only, will reverse the phrasing, and say that only 

 such changes as are effected exclusively by the vital action of ferments come within 

 the meaning of the term fermentation. The point of the definition, as already 

 mentioned at the commencement of the previous paragraph, lies in the words 

 italicised. 



However equivalent the action of purely inorganic force on the one hand, 

 and of living organisms on the other may appear, it is so in regard to quality 

 only, the quantitative effects, the amount of substance decomposed in unit time, 

 being widely different. Regarded from this point of view, the minute ferments 

 appear as centres for the accumulation of high-tension energy, by the release of 

 which force the decomposition in view can be effected, not only in a shorter time, 

 but also in a more restricted space, than is possible by the action of purely 

 chemical forces. 



