480 ZOOLOGY 



Researches 3. It was during this period that Pasteur made his 

 first scientific discovery. There is an instrument called 

 the polariscope, which may be used to test the strength 

 of various substances in solution, such as sugar or tar- 

 taric acid compounds. The rays of light, passing 

 through the apparatus, are deflected to the right or left, 

 according to the nature of the substance used. The 

 chemists had worked out a theory of polarization, but 

 there remained a stumbling-block, which no one had 

 been able to remove. Paratartrate solutions, quite con- 

 trary to expectation, were neutral, deflecting the light 

 neither this way nor that. We said that Pasteur early 

 exhibited scientific caution, but this means only that 

 he worked carefully, making sure of each step. He had 

 little or none of that so-called caution which frightens 

 a man away from a difficult task. The fact that 

 others had failed was for him a reason for attacking a 

 problem. So he took up the paratartrate puzzle, and 

 presently discovered that when the substance crystal- 

 lized out, the crystals were not all alike. They were 

 asymmetrical, and one set was the reverse or looking- 

 glass image of the other. Did this mean anything ? 

 Separate solutions were made of the two kinds, and 

 immediately the problem was solved. One kind rotated 

 the light to the right, the other to the left, and when 

 they were mixed, they neutralized "each other! How 

 very simple ! but none of the chemists who had 

 previously investigated the subject had thought of it. 



Pasteur and 4. There was an old and eminent chemist in Paris, 

 named J. J. Biot. On hearing of Pasteur's discovery 

 he expressed incredulity, and wished to see the thing for 

 himself. So one day the young man called at the 

 College de France, and was admitted into Biot's labora- 

 tory. Biot himself prepared the materials ; he would 



