Supplement ot "Nature" December 23, 1922 



of Arbois, he proceeded to Besancon and entered the 

 Ecole Normale in 1843. Here, as a student of chemistry, 

 he came under the influence of Balard and of Dumas, 

 while his attention was turned to crystallography by 

 M. Delafosse, assistant to Haiiy. When in 1844 Biot 

 presented to the French Academy of Sciences a paper 

 by Mitscherlich, in which it was stated that the sodium 

 ammonium salts of racemic acid and of ordinary 

 tartaric acid respectively were identical not only in 

 chemical composition but also in crystalline form, 

 Pasteur, who seems to have been guided by Sir John 

 Herschel's discovery in 1820 of the opposite hemi- 

 hedral relationship of dextro- and laevo-rock crystal 

 or quartz, demonstrated to Biot's satisfaction that the 

 crystals of sodium ammonium racemate also exhibited 

 opposite hemihedrism. He was able, in fact, to separate 

 by selection those crystals derived from ordinary dextro- 

 tartaric acid and those derived from the hitherto un- 

 known laevo-tartaric acid. Pasteur was, however, in 

 the first place a chemist, and not long afterwards he 

 discovered a chemical means of resolving racemic acid 

 into its enantiomorphic isomerides by fractional 

 crystallisation of its salts with certain optically active 

 bases. This was followed later by a third, a biochemical 

 method, which depended on the fact that the green 

 mould Penicillium glaucum, when grown in the presence 

 of racemic acid, ferments the dextro-acid preferably 

 to the Iaevo-acid. 



It is possible that this last-mentioned discovery was 

 the means of leading Pasteur into the domain of 

 biology, in which branch of science he was destined 

 to make such brilliant discoveries. The commence- 

 ment of his researches on yeast dates, however, from 

 the year 1856, when he occupied the position of Dean 

 of the Faculty of Science at Lille. Here he was con- 

 sulted by a local distiller named Bigo on certain 

 difficulties encountered in the manufacture of alcohol 

 from beetroot. 



Before describing Pasteur's final conclusions on the 

 nature of yeast and of alcoholic fermentation, it will 

 be necessary to take a brief retrospective glance on 

 the state of our knowledge prior to the period with 

 which we are dealing. 



The cellular form of yeast had been established so 

 long ago as the seventeenth century by Anton Van 

 Leeuwenhoek, and in 1836 Cagniard-Latour observed 

 that yeast cells are susceptible of reproduction by a 

 sort of budding, while a similar observation was made 

 about the same time by Schwann. Little account was 

 taken of these observations, however, and alcoholic 

 fermentation was explained by the theories of Berzelius 

 and of Liebig, the former regarding it as a catalytic 

 phenomenon, and the latter as one in which the ferment 

 (yeast) was a substance which decomposed readily, 



and in so doing set in motion the molecules of the 

 fermentative matter. 



In the year 1856, Pasteur commenced his studies on 

 yeast and on alcoholic fermentation, and from that 

 time dates his celebrated controversy with Liebig, 

 which raged with fury up to the year 1861, when 

 Pasteur had established anaerobic growth in certain 

 micro-organisms, and had finally proved that yeast is 

 a living organism. His further conclusion was that 

 alcoholic fermentation is a phenomenon coterminous 

 with the life of yeast. Still Liebig maintained his 

 view tenaciously, and only modified it in 1870. 



" It is possible," said Liebig, " that the only correla- 

 tion between the physiological act and the phenomenon 

 of fermentation is the production in the living cell of 

 the substance which, by some special property analogous 

 to that by which emulsin exerts a decomposing action 

 on salicin and amygdalin, may bring about this decom- 

 position of sugar into other organic molecules ; the 

 physiological act, in this view, would be necessary for 

 the production of this substance, but it would have 

 nothing else to do with fermentation." To this 

 Pasteur replied, " Ici je ne contredirais encore pas." 



Liebig's final hypothesis was therefore similar if 

 not identical with that of Berzelius, and we shall now 

 see how it was reconciled ultimately with the views of 

 Pasteur. Berthelot in 1858 suggested that fermenta- 

 tion was the result of unorganised ferments (enzymes) 

 secreted by the yeast, but to this Claude Bernard 

 objected in i860. Brefeld in 1874-75 considered that 

 it was only when all the free oxygen in a fermentable 

 liquid had been removed that the yeast cells commenced 

 to excite fermentation, which he believed to be due to 

 an enzyme. Pasteur in the course of his work had 

 tried in vain to isolate this enzyme, and he favoured 

 the view that fermentation was a vital act of the yeast 

 cell. In 1897 E. Buchner extracted the enzyme of 

 alcoholic fermentation from yeast and called it zymase. 



Pasteur's further work on fermentation is embodied 

 in his celebrated treatise, " Etudes sur la biere " 

 (1876). 



" Our misfortune," he says, " prompted me with the 

 idea of these researches. I undertook them immedi- 

 ately after the war in 1870, and have since continued 

 them without interruption, with the determination of 

 perfecting them, and thereby benefiting a branch of 

 industry wherein we are undoubtedly surpassed by 

 Germany. I am convinced that I have formed a 

 precise, practical solution of the arduous problem 

 which I proposed to myself — that of a process of 

 manufacture, independent of season and locality, 

 which should obviate the necessity of having recourse 

 to the costly methods of cooling employed in existing 

 processes, and at the same time secure the preservation 

 of its products for any length of time." 



Pasteur's views on alcoholic fermentation are some- 

 what difficult to understand ; hence he met with manv 



