40 LOUIS PASTEUR 



of albuminous material. Like the calcium salt, it 

 was found to ferment. He tried the same experi- 

 ment with ammonium paratartrate which, it will be 

 remembered, is a mixture of right-handed and left- 

 handed tartrates. This solution, at first optically 

 inactive, was found, as fermentation went on, to 

 rotate the polarized ray more and more to the left. 

 When the fermentation stopped, the right-handed 

 tartrate had disappeared; only the left-handed tar- 

 trate remained. The fluid, originally clear, was 

 now clouded, owing, as was shown by the micro- 

 scope, to the presence of minute living organisms. 

 The microscopic forms of life selected as food the 

 one asymmetrical tartrate, and left the other, 

 thereby suggesting a peculiar asymmetry of their 

 own protoplasm, which made it possible for it to 

 act chemically on but one of the two constituents 

 of the solution. 



Doubtless this discovery confirmed Pasteur in 

 his views regarding the asymmetry of the com- 

 pounds that are immediately concerned with vital 

 activity. What is of especial importance for his 

 future career is that it took him across the bound- 

 ary that separated chemistry and biology. Hence- 

 forth, it was the micro-organisms which were to 

 form the chief object of his research. 



