A LABORIOUS YOUTH 35 



France, where Biot lived. Every slightest de- 

 tail of that interview must have remained fixed 

 forever in Pasteur's memory. Biot began by 

 going in search of paratartaric acid. 



" 'I have studied it/ he said, 'with particu- 

 lar care: it is perfectly neutral in relation to 

 polarised light/ A tinge of mistrust was visi- 

 ble in his gestures and betrayed itself in the 

 tone of his voice. 'I will bring you everything 

 you need/ continued the old man as he went in 

 quest of the required quantities, of soda and 

 ammonia. He desired that the double salt 

 should be prepared in his presence. 



"After pouring the liquid obtained into the 

 crystalliser, Biot took it and set it aside in one 

 corner of his apartment, in order to be quite 

 sure that no one would touch it. 'I will notify 

 you when you are to come back/ he said to Pas- 

 teur as he ushered him out. Forty-eight hours 

 later the crystals, very small at first, began to 

 take form. When there appeared to be a suffi- 

 cient quantity of them Pasteur was summoned. 

 Still in the presence of Biot, Pasteur drew out 



