34 PASTEUR: THE HISTORY OF A MIND 



always had the good fortune never to wander very 

 far from the right path. His adventurous spirit led 

 him sometimes to the right or to the left of it, as he 

 followed the trail, but he always recovered the true path. 

 It is in these moments when he walked hand in hand 

 with truth that we must lay hold of him: they are the 

 landmarks of his route and of his career. 



The theoretical idea which I have just pointed out 

 prevented him from believing that the inactive malic 

 acid was a paratartaric acid. Consequently, it must 

 present a new atomic grouping in which the optical 

 inactivity results not from a compensation between 

 equal and opposed forces but from the disappearance 

 of all dissymmetry in the active molecule. It was very 

 audacious to imagine a new theoretical grouping when 

 there were already three, but Pasteur had audacity and 

 this audacity had often served him well. The malic 

 acid which he studied was not, we have said, the com- 

 pound with the symmetrical structure, which he had 

 dreamed it to be. Nevertheless he was not absolutely 

 deceived, for this body with a symmetrical structure 

 exists in the tartaric series, as Pasteur himself was to 

 discover a little later. 



Here is another point where error did not prevent him 

 from arriving at the truth. Confident in his idea that 

 he had an aspartic acid and a malic acid with a sym- 

 metrical molecule not contorted, so to speak, he made a 

 careful comparison of these acids with the twisted and 

 dissymmetrical molecules obtained from asparagin and 

 the fruit of the sorb-tree. He wished to see how this 

 symmetry or dissymmetry of the molecule expressed 

 itself externally, in the physical and chemical characters 

 of the acids and their salts. 



From this study he derived no definite knowledge for 

 two reasons. The first is that the substances to which he 



