38 LOUIS PASTEUR. 



ments are almost always microscopic vegetables, which 

 embrace in their constitution cellulose, albumen, &c., 

 identical with these same substances taken from the 

 higher class of vegetables and equally dissymmetric. 

 We can thus understand, that for the nutrition of the 

 ferment and the formation of its principles the 

 chemical changes are more easy with one of the two 

 tartaric acids than with the other. 



The opposition of the properties of the two tartaric 

 acids, right and left, at the moment when the condi- 

 tions of life and nutrition of an organised being inter- 

 vened, showed themselves still more strikingly in a 

 very curious experiment made by Pasteur. He was the 

 first to prove that mildew could live and multiply on 

 a purely mineral soil, composed, for example, of the 

 phosphates of potash, of magnesia, and an ammoniacal 

 salt of an organic acid. For such a development of vege- 

 table life he employed the seed of penicillium glaucum, 

 which is to be found everywhere as common mould, 

 and to which he offered, as its only carbon aliment, 

 paratartaric acid. At the end of a little time the left- 

 handed tartaric acid appeared. Now this left-handed 

 acid could only show itself on the condition that a 

 rigorously equal quantity of the right-handed acid had 

 been decomposed. The carbon of the tartaric acid 

 evidently supplied to the little plant the carbon that 

 was necessary for the formation of its constituents and 

 all their organic accessories. If the microscopic seed 



