362 TIMOTHY RICHARDS LEWIS. 



and shortly afterwards. The discovery at this time of the yeasjt- 

 plant by Schwann and Cagniard-Latour soon led to the more 

 general recognition of the almost constant association of certain 

 low organisms with different kinds of fermentations. But it was 

 not till twenty years afterwards that Pasteur announced, as the 

 result of his apparently conclusive researches, that low organisms 

 acted as the invariable causes of fermentations and putrefactions ; 

 that such changes, in fact, though chemical processes, were only 

 capable of being initiated by the agency of Hving units.''' These 

 observations and the interpretations applied to them very rapidly 

 caught the ear of the medical profession, as from a very early 

 period in the history of medicine the supposition that disease was 

 propagated by means of a ferment — a leaven — had taken a firm 

 hold. Previous to the publication of M. Pasteur's observations, 

 a physico-chemical theory had been almost universally acknow- 

 ledged as sufficiently explanatory of the phenomena manifested 

 by certain classes of disease. This was notably the case with 

 regard to the fermentation-doctrine of Liebig, a doctrine the 

 truth of which he strongly advocated until the day of his death 

 in 1873, and which, somewhat modified as a result of later 

 researches, is still upheld by some of the most eminent chemists 

 of our own time. 



The leading features the " vital" and the '' physico-chemical " 

 theories of fermentation^ have recently been lucidly summarised 

 by Mr. C. T. Kingzett in a paper read before the Society of 

 Arts.^ With regard to the first of these views and in illustration 

 of them this chemist remarks : " When a solution of sugar is 

 exposed to the action of healthy yeast it suffers a change; the 

 atoms comprised in its molecules are broken up and rearranged 

 into new forms, which are recognised as alcohol and carbonic 

 dioxide. Glycerine and succinic acid are also formed at the 

 expense of the sugar, but the lactic acid which generally accom- 

 panies alcoholic fermentation is considered as proved to be due to 

 the presence of a ferment distinct from, but accompanying, the 



1 ' Certain organic compounds, when exposed to the action of air, water, 

 and a certain temperature, undergo decomposition, consisting either in a 

 slow combustion oroxidation by the surrounding air, or in a new arrange- 

 ment of tlie elements of the compound in different proportions (often with 

 assimilation of tlie elements of water), and the consequent formation of new 

 products. The former process, that of slow combustion, is called Erema- 

 camis or Decay ; the latter is called Putrefaction or Fermentation — putre- 

 faction when it is accompanied by an offensive odour, ferme?itation when no 



such odour is evolved, and especially if the process results in the formation 

 of useful products ; thus, the decomposition of a dead body, or of a quantity 

 of blood or urine, is putrefaction ; that of grape-juice or 'malt-wort, which 

 yields alcohol, is fermentation.' — ' Watt's Diclionarv of Chemistry,' vol. ii 

 p. 024, 1872. 



2 'Journal of the Society of Arts,' March, 1878. 



