Supplement to "Nature," December 23, 1922 



combine molecularly to form compounds of racemic 

 character. His methods and his law have thus come 

 to be of wide, indeed general, application to all such 

 cases. With regard to the deeply interesting question 

 why so slight a difference of nature, between two 

 varieties of a substance, as a mere difference of type 

 of helix — right- or left-handed — along which the atoms 

 are arranged, should be a sufficient cause for the 

 different behaviour of a living organism brought into 

 contact with it, remains still unsolved. The fact, 



however, has been amply confirmed over and over 

 again, as well as by Emil Fischer's results on the 

 selective fermentation of sugars by yeasts, so that it 

 appears as if the action of every living organism 

 corresponds to only a particular arrangement of the 

 atoms in a chemical molecule. Pasteur himself says 

 (i860), and with these words of still valid portent this 

 article may well conclude : " II y a la des myst£res, qui 

 preparent a l'avenir d'immenses travaux et appellent des 

 aujourd'hui les plus serieuses meditations de la science." 



Pasteur's Early Research in Pure Chemistry and Fermentation. 



By Prof. Arthur Harden, F.R.S. 



THE purely chemical researches of Pasteur, under- 

 taken when he was a young man of twenty-two 

 years of age, were all comprised within the epoch 

 1 844-1 860, during the latter part of which he was also 

 actively engaged on his great work on fermentation. 

 Pasteur's fundamental contribution to pure chemistry, 

 the idea of the asymmetric arrangement of the atoms 

 within the molecule, has proved to be one of the most 

 fruitful conceptions of the science. The experimental 

 methods which led to its development have provided 

 chemists with a weapon by which many of the most 

 difficult and subtle problems have been successfully 

 attacked ; a weapon which still maintains its place in 

 the armoury of the chemist and is every day turned to 

 fresh account. 



Pasteur's fundamental experiment on the resolution 

 of the racemates, and the dramatic scene in which his 

 great discovery was recognised by the veteran Biot, 

 are among the classics of chemical literature. The 

 thrill accompanying the culmination of this his first 

 successful research, the memory of that joyous nervous 

 excitement which prevented him from again looking 

 into the polarimeter, must have always remained 

 vividly present to his mind and can never have been 

 effaced even by the ever-increasing flood of discoveries 

 which marked his later years. 



Stereochemical relations are now so well established 

 and so universally admitted that it is difficult to realise 

 the intrepidity of Pasteur's theoretical deductions. 

 Ik- saw at once that the asymmetry of his two tartaric 

 acids would lead them to form different compounds 

 with an asymmetric (optically active) base. On 

 making the experiment, after many abortive attempts, 

 he at length had the satisfaction, second only to that 

 experienced at the successful resolution of the race- 

 mates, of obtaining crystals of pure cinchonicine 

 laevotartrate by the crystallisation of the racemate of 

 this optically active base. Thus was established the 

 classical chemical method for the resolution of asym- 

 metric compounds. 



It is of special interest, in view of the later direction 



of Pasteur's scientific work, that he at once perceived 

 the bearing of his new discoveries on the chemistry 

 of the living organism. It was only among the pro- 

 ducts of vegetable and animal life that he found 

 substances the molecules of which were asymmetric. 

 In the mineral kingdom and among the synthetic 

 products of the organic chemist molecular symmetry 

 held undisputed sway. He therefore regarded the 

 living organism as the sole source of asymmetric 

 molecules, the cell acting as " a laboratory of asym- 

 metric forces." Observation soon reinforced these 

 theoretical ideas. Struck by the " spontaneous " 

 fermentation of a solution of ammonium tartrate, he 

 transferred a drop of the fermenting liquid to a solution 

 of ammonium racemate and found that when the 

 fermentation which ensued had ceased the laevotartrate 

 was quite intact whereas the dextro-acid had dis- 

 appeared. " Thus " says Pasteur, in his lectures 

 on Asymmetry, 1 i860, " the conception of the influence 

 of the molecular symmetry of natural organic products 

 is introduced into physiological studies through this 

 important criterion (optical activity), which forms 

 perhaps the only sharply defined boundary which can 

 at the present day be drawn between the chemistry 

 of dead and living nature." 



It was, according to Duclaux in his charming bio- 

 graphy " Pasteur, histoire d'un esprit," another 

 aspect of the relation between organisms and the 

 asymmetry of their products which led him to the 

 study of fermentation, his next great field of discovery. 

 Amyl alcohol, the optically active constituent of fusel 

 oil, was at that time universally supposed to be derived 

 from the sugar, although it is now known, through the 

 brilliant researches of Felix Ehrlich, to be a product 

 of the decomposition of protein. This substance was 

 assumed by the opponents of the vitalistic theory of 

 fermentation, which had been based on the discovery 

 of the living nature of yeast in 1837, to owe its optical 

 activity to the parent molecule of sugar from which it 



1 Quoted from Frankland's Pasteur Memorial Lecture, Jour. Chem. 



