LIEBIG'S DECOMPOSITION THEORY. 19 



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. decomposi- 

 tion, 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 decompos- 

 ing 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 undecomposed substance. Consequently this function has 

 to be performed by an extraneous 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 differentiation 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, con- 

 tinues 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 satis- 

 factorily 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 de- 

 posited 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 con- 

 tinuance of fermentation; only, the ferment is degraded to a 

 simple albuminoid substance. To enter now-a-days into a further 



