xiv 



acid which were destitute of these little surfaces were symmetrical, 

 the crystals of the optically active tartaric acid were unsymmetrical, 

 or dissymmetric, as he called it. Now, to the symmetric character of 

 the crystals of the one tartaric acid, generally known as paratartaric 

 or racemic acid, he attributed the inactivity of this tartaric acid to 

 polarised light ; whilst with the dissymmetric character of the crys- 

 tals of the other tartaric acid he connected its action on the polarised 

 beam. In studying these apparently trifling details, Pasteur found 

 that by crystallising the inactive tartaric acid in a particular way, 

 by preparing the sodium ammonium salt and crystallising this, he 

 obtained two different kinds of crystals — the one set being identical 

 with those of the active tartaric acid already known, whilst the other 

 set were the mirror images of these and had never been seen by the 

 eye of man before. The young philosopher at once drew the con- 

 clusion that if the dissymmetry of the known tartaric acid caused it 

 to turn the plane of polarisation to the right, the dissymmetry of 

 this new tartaric acid should turn it to the left. 



With infinite pains Pasteur picked out from the mixture the 

 individual crystals belonging to each of the two types, and arranged 

 them in two heaps. Each of these heaps of crystals was then 

 separately dissolved in water, and the two solutions submitted to 

 polarised light. In accordance with his anticipation, whilst the 

 solution of the crystals of the known form was found to turn the 

 plane of polarisation to the right, the solution of the new crystals, 

 the mirror images of the old, was found to tarn the plane through 

 precisely the same angle to the left. 



Of such moment did this discovery appear to Pasteur that, rush- 

 ing from the laboratory in a fever of excitement, and meeting M. 

 Bertrand in the corridor he embraced him, exclaiming, overcome 

 with emotion : " Je viens de faire une grande decouverte ;" and such 

 indeed it was ; but it is related how, whilst producing a great sensa- 

 tion in scientific circles, it was received with no little scepticism by the 

 Academy of Sciences who instructed Biot to report upon it. Pasteur 

 has himself described the sceptical and almost suspicious attitude 

 adopted by this great investigator towards the work of this enthu- 

 siastic novice in the regions of scientific research, and how, as step 

 Toy step Biot verified the accuracy of Pasteur's observations, he 

 became more and more excited until, finally, when he found that the 

 solution of the new crystals, as Pasteur had affirmed, exhibited a 

 strong lsevo-rotation in the polarimeter, he seized him by the hand, 

 exclaiming with visible emotion, " Mon enfant, j'ai taut aime les 

 sciences dans ma vie que cela me fait battre le cceur." 



Pasteur proceeded to point out that the differences in optical pro- 

 perties and in crystalline form exhibited by these two oppositely 

 active tartaric acids were doubtless dependent on the two molecules 



?2 



