LIEBIG'S DECOMPOSITION THEORY 15 



substances outside the animal or vegetable body of whose vital functions they 

 are the outcome. That organic substances could not be produced without the 

 concurrence of vital power was up till that time an established maxim. To 

 overthrow this dogma, and to prove that any desired organic substance can be 

 prepared without the assistance of vital action, was the endeavour of the 

 majority of the chemists of the age, Liebig being one of the foremost, most 

 industrious, and stubbornest workers in the cause. It is, therefore, small 

 matter for astonishment that Cagniard-Latour, Kiitzing, and Schwann to 

 the contrary, notwithstanding he could conceive a theory of fermentation 

 wherein the action of living organisms had no place and their vital force was 

 ignored. 



The struggle against what he considered to be the objectionable theory of 

 these three physiologists was opened by Liebig in 1839 with an anonymous 

 treatise (I.), in which the new observations of the microscopists were covered 

 with highly amusing satire. In the next year he returned to the charge in 

 earnest in his work on " Organic Chemistry in Relation to Agriculture and 

 Physiology," on pp. 202-299 of which his new theory is enunciated. This is, as 

 already mentioned, akin to that put forward by Stahl more than a century 

 before. 



Liebig considered all fermentation as molecular movement, which a body in 

 a state of chemical movement, i.e. decomposition, transfers to other substances 

 whose elements are not very firmly combined. Between fermentation (in its 

 limited sense) and putrefaction there is the following difference : In the latter 

 putrefaction the decomposition is transmitted by the decomposing material 

 viz., the albuminoids so that putrefaction, once begun, is continued by inherent 

 movement, even though the initial cause has been rendered inactive. With 

 fermentation it is otherwise. In this process the body (sugar) in a state of 

 incipient decomposition cannot transmit the movement to the still undecom- 

 posed substance. Consequently this function has to be performed by an extra- 

 neous causative agent, a ferment, which in this case is necessary not only for 

 commencing (as with putrefaction), but also for continuing the decomposition. 



It must be admitted that, at first sight, this definition, as also the differentia- 

 tion between fermentation and putrefaction, is very attractive. Nevertheless 

 it will not bear the light of keen criticism. Take, in the first place, the character 

 on which the distinction between fermentation and putrefaction is based, viz., 

 that the former will not go on without the presence of the ferment, whereas, 

 on the other hand, putrefaction, when once started, continues spontaneously, 

 the ferment being no longer needed. The reason why Liebig was induced to 

 make this distinction is easy to fathom. In the case of fermenting beer- 

 wort which Liebig usually had in view when speaking of fermentation 

 the ferment (beer-yeast) was discernible to the naked eye, and experience 

 taught that without this ferment the fermentation could not be satisfactorily 

 carried on. On the other hand, the presence of those minute organisms which, 

 as we now know, insinuate themselves into all substances liable to putrefaction, 

 and decompose the same without, as a rule, giving rise to such a multiplication 

 of the deposited ferment as can be remarked by the inexpert eye, is not so 

 immediately apparent as in alcoholic fermentation. 



Thus, even in Liebig's opinion, yeast is essential to the continuance of 

 fermentation ; only, the ferment is degraded to a simple albuminoid substance. 

 To enter nowadays into a further onslaught against this theory would be 

 merely storming an undefended position. Moreover, as the subsequent editions 

 of the aforesaid work demonstrate, it was gradually modified by its author, so 

 that the form in which it was presented in his latest exposition (II.) in 1870 

 differs in many particulars from the original. 



