xlvii 



racemic acid into its component dextro- and laevo-tartaric acids by 

 means of optically active bases, and his famous refutation of Des- 

 saignes' reputed conversion of f umaric and male'ic acids into aspartic 

 acid, identical with that hitherto only obtained from asparagine. 



Pasteur had himself studied these various bodies before the publi- 

 cation of Dessaignes' memoir, and he had found that whilst fumaric 

 and maleic acids were not dissymmetric and were destitute of all 

 optical activity, aspartic acid, on the other hand, like asparagine, 

 from which it is derived, was endowed with molecular dissymmetry, 

 and was active towards polarised light. 



If Dessaignes' facts were correct, they would mean that he had 

 accomplished what Pasteur firmly believed to be impossible — the 

 preparation by artificial chemical means of an optically active mole- 

 cule from an inactive one. Pasteur, with his usual restless energy, 

 determined at once to set this doubt at rest, and hurrying to 

 Vendome he obtained from Dessaignes a specimen of his artificial 

 aspartic acid. On returning to his laboratory, Pasteur examined it 

 with the minutest care, and found that, in spite of its great resem- 

 blance to the acid derived from asparagine, it differed in a very im- 

 portant particular,- inasmuch as it was entirely devoid of the action 

 on polarised light which characterised the former, and he had no 

 difficulty in showing that Dessaignes' acid was not identical with the 

 natural aspartic acid, but only its inactive isomeride. 



So far Pasteur had kept strictly to the domain of pure chemistry 

 and molecular physics, and his attention was entirely absorbed by 

 problems which, while of profound theoretical interest, gave no 

 indication of the direction which his future labours would take, 

 and to the pursuit of which his whole life was subsequently to be 

 devoted. 



It was an incident, trifling in itself, which first suggested to 

 Pasteur the application of fermentation processes to the study of 

 chemical substances. His attention having been called to a chance 

 observation made by a German firm of manufacturing chemists, that 

 solutions of impure commercial tartrate of lime fermented when left 

 in warm weather in contact with organic matters, he determined at 

 once to utilise this fact and induce, if possible, fermentation in a 

 solution of ordinary right-handed tartaric acid. Dissolving a salt 

 of this acid, he added to the solution a small quantity of albumen 

 with the result that fermentation ensued and the liquid, originally 

 clear, became gradually turbid, a phenomenon which Pasteur found 

 was due to the presence of small living cells, upon which he subse- 

 quently showed the process of fermentation to be dependent. This 

 method he also applied to solutions of the paratartrate (racemate) 

 with the same results. On examining the solutions, after fermenta- 

 tion, with the polarimeter, the most profound difference was found 



