IV 



YEAST 11' 



complete conception of the nature of the work to 

 be done. The words in which he expresses this 

 conception, in the treatise on elementary chemistry 

 to which reference has already been made, mark 

 the year 1789 as the commencement of a revolu- 

 tion of not less moment in the world of science 

 than that which simultaneously burst over the 

 political world, and soon engulfed Lavoisier himself 

 in one of its mad eddies. 



"We may lay it down as an incontestable axiom that, in all 

 the operations of art and nature, nothing is created ; an equal 

 quantity of matter exists both before and after the experiment : 

 the quality and quantity of the elements remain precisely the 

 same, and nothing takes place beyond changes and modifications 

 in the combinations of these elements. Upon this principle the 

 whole art of performing chemical experiments depends ; we 

 must always suppose an exact equality between the elements of 

 the body examined and those of the products of its analysis. 



"Hence, since from must of grapes we procure alcohol arid 

 carbonic acid, I have an undoubted right to suppose that must 

 consists of carbonic acid and alcohol. From these premisses we 

 have two modes of ascertaining what passes during vinous fer- 

 mentation : either by determining the nature of, and the elements 

 which compose, the fermentable substances ; or by accurately ex- 

 amining the products resulting from fermentation ; and it is evi- 

 dent that the knowledge of either of these must lead to accurate 

 conclusions concerning the nature and composition of the other. 

 From these considerations it became necessary accurately to 

 determine the constituent elements of the fermentable sub- 

 stances ; and for this purpose I did not make use of the com- 

 pound juices of fruits, the rigorous analysis of which is perhaps 

 impossible, but made choice of sugar, which is easily analysed, 

 and the nature of which I have already explained. This sub- 

 Btance is a true vegetable oxyd, with two bases, composed of 



