VIII 



SUBSTANCES INACTIVE THROUGH LOSS OF 

 DISSYMMETRY 



We are going to discover a new proof of the certainty 

 of Pasteur's intuition. Starting with asparagin, and 

 profiting by the labors of Piria, we have seen that we 

 can obtain products more and more simplified: aspartic 

 acid, malic acid, maleic acid, and fumaric acid. In 

 this continued degradation of the asparagin molecule 

 there is a point reached where the molecular dissym- 

 metry disappears, permanently: this is at the maleic 

 or fumaric acid boundary. But it happened in 1850 

 that M. Dessaignes, an able chemist of Vendome, 

 succeeded in following inversely the steps of Piria, and 

 of remounting by the chemical path from malic acid 

 to aspartic acid, then, some months later, from fumaric 

 and maleic acids to the same aspartic acid. 



The passage from malic acid to aspartic acid had not 

 surprised Pasteur, both of them being active on polarized 

 light, but the case was different with maleic acid. In 

 transforming this into malic or aspartic acid, Dessaignes 

 would have created an active molecule by a laboratory 

 operation. This would have been, in the eyes of Pasteur, 

 a great discovery. He must assure himself of the truth 

 of it at once. 



Pasteur, therefore, hastened to Vendome to state his 

 scruples to Dessaignes, and obtained from him without 

 difficulty a sample of the new aspartic acid which he made 

 haste to study. As he had expected, he did not find 

 any rotary power: this acid was an inactive acid. But 

 it resembled so much, in all its physical and chemical 



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