38 THE LIFE OF PASTEUR 



" You say," wrote his father on April 28, 1848, " that you 

 have offered to France all your savings, amounting to 150 

 francs. You have probably kept a receipt of the office where 

 this payment was made, with mention of the date and place? " 

 And considering that this action should be made known, he 

 advises him to publish it in the journal Le National or La 

 RS forme in the following terms, " Gift to the Patrie : 150 

 francs, by the son of an old soldier of the Empire, Louis 

 Pasteur of the Ecole Normale." He wrote in the same letter, 

 " You should raise a subscription in your school in favour of 

 the poor Polish exiles who have done so much for us ; it would 

 be a good deed." 



After those days of national exaltation, Pasteur returned to 

 his crystals. He studied tartrates under the influence of 

 certain ideas that he himself liked to expound. Objects con- 

 sidered merely from the point of view of form, may be divided 

 into two great categories. First, those objects which, placed 

 before a mirror, give an image which can be superposed to 

 them : these have a symmetrical plan ; secondly , those which 

 have an image which cannot be superposed to them : they are 

 dissymmetrical. A chair, for instance, is symmetrical, or a 

 straight flight of steps. But a spiral staircase is not sym- 

 metrical, its own image cannot be laid over it. If it turns to 

 the right, its image turns to the left. In the same way the 

 right hand cannot be superposed to the left hand, a righthand 

 glove does not fit a left hand, and a right hand seen in a mirror 

 gives the image of a left hand. 



Pasteur noticed that the crystals of tartaric acid and the 

 tartrates had little faces, which had escaped even the profound 

 observation of Mitscherlich and La Provostaye. These faces, 

 which only existed on one half of the edges or similar angles, 

 constituted what is called a hemihedral form. When the 

 crystal was placed before a glass the image that appeared could 

 not be superposed to the crystal ; the comparison of the two 

 hands was applicable to it. Pasteur thought that this aspect 

 of the crystal might be an index 'of what existed within the 

 molecules, dissymmetry of form corresponding with molecular 

 dissymmetry. Mitscherlich had not perceived that his tartrate 

 presented these little faces, this dissymmetry, whilst his para- 

 tartrate was without them, was in fact not hemihedral. There- 

 fore, reasoned Pasteur, the deviation to the right of the plane 

 of polarization produced by tartrate and the optical neutrality 



