1844—1849 41 



fixed in Pasteur's memory. Biot began by fetching some 

 paratartaric acid. " I have most carefully studied it," he said 

 to Pasteur ; " it is absolutely neutral in the presence of polarized 

 light." Some distrust was visible in his gestures and audible 

 in his voice. "I shall bring you everything that is neces- 

 sary," continued the old man, fetching doses of soda and 

 ammonia. He wanted the salt prepared before his eyes. 



After pouring the liquid into a crystallizer, Biot took it into 

 a corner of his room to be quite sure that no one would touch it. 

 " I shall let you know when you are to come back," he said to 

 Pasteur when taking leave of him. Forty-eight hours later 

 some crystals, very small at first, began to form; when there 

 was a sufficient number of them, Pasteur was recalled. Still in 

 Biot's presence, Pasteur withdrew, one by one, the finest 

 crystals and wiped off the mother-liquor adhering to them. He 

 then pointed out to Biot the opposition of their hemihedral 

 character, and divided them into two groups — left and right. 



" So you affirm," said Biot, " that your righthand crystals 

 will deviate to the right the plane of polarization, and your 

 lefthand ones will deviate it to the left? " 



" Yes," said Pasteur. 



"Well, let me do the rest." 



Biot himself prepared the solutions, and then sent again for 

 Pasteur. Biot first placed in the apparatus the solution which 

 should deviate to the left. Having satisfied himself that this 

 deviation actually took place, he took Pasteur's arm and said 

 to him these words, often deservedly quoted : " My dear boy, I 

 have loved Science so much during my life, that this touches 

 my very heart." 



"It was indeed evident," said Pasteur himself in recalling 

 this interview, " that the strongest light had then been thrown 

 on the cause of the phenomenon of rotatory polarization 

 and hemihedral crystals ; a new class of isomeric substances 

 was discovered ; the unexpected and until then unexampled 

 constitution of the racemic or paratartaric acid was revealed ; 

 in one word a great and unforeseen road was opened to science." 



Biot now constituted himself the sponsor in scientific matters 

 of his new young friend, and undertook to report upon Pasteur's 

 paper entitled : " Researches on the relations which may exist 

 between crystalline form, chemical composition, and the 

 direction of rotatory power " — destined for the Academie des 

 Sciences. 



