54 RESPIRATION 



process and regarded alcohol neither as a constituent of the 

 grapes nor as a product of fermentation. Instead he considered 

 it to arise by the reciprocal action of the sugar and the glutenous 

 material. 



The chemical studies of Lavoisier (1789) on fermentation led 

 him to conclude that sugar was merely separated into two constit- 

 uents, carbon dioxide and alcohol, and that if the two were re- 

 united, sugar would be reconstructed. He thought that one con- 

 stituent was oxygenated at the expense of the other, that the oxy- 

 genated portion became carbon dioxide, and that the deoxy- 

 genated portion became alcohol. 



Thenard (1802-1803) made the interesting observation that a 

 deposit resembling yeast occurred during fermentation of the 

 juice of gooseberries, cherries, apples, or other fruits. When this 

 deposit was mixed with fresh juice, fermentation was started. He 

 was unable to determine whether this deposit came into existence 

 from a soluble state or whether it Mas a product of fermentation. 



In 1838 the classical work of Cagniard-Latour (1838), in which 

 he described his microscopic studies of yeast, appeared. He stated 

 that the globules which he found in wine and beer constituted 

 the yeast and belonged to the vegetable kingdom. He correctly 

 described their propagation by budding, the buds at first being 

 small and attached to the mother cell. 



While Cagniard-Latour was making his discoveries, Schwann 

 (1837) examined the deposit in beer and in grape juice and came 

 to the conclusion that this deposit was yeast and that yeast was a 

 fungus. He clearly established the relationship of yeast to fer- 

 mentation by the following phenomena: (a) the constancy of 

 occurrence of yeasts during fermentation, and (b) the checking 

 of fermentation by heat, chemicals, or other agencies that destroy 

 living organisms. According to him, alcohol was a waste product 

 left as the yeast drew its food from the sugary solution. Schwann 

 must properly be credited with founding the germ theory or 

 biological theory of fermentation. 



.Meanwhile the chemical theory of fermentation had its adher- 

 ents in such capable chemists as Berzelius and Liebig. They held 

 up to contemptuous ridicule the work of Cagniard-Latour, 

 Schwann, and all others, notably Kiitzing, who believed that 

 veasts produce fermentation. Liebig and his pupils [Bulloch 



