SELECTED PAPERS 



it lives. Striking examples of this sort have become known, especially 

 during recent years, and they do not suffer from a lack of technological 

 significance. 



A first instance may be derived from an investigation of the Ameri- 

 can microbiologist, Currie. Whereas oxalic acid, in addition to carbon 

 dioxide, had been found as a significant by-product of the carbo- 

 hydrate metabolism of the intensively studied mould, Aspergillus niger, 

 Currie succeeded in demonstrating that the oxidation of carbohydrates 

 by this mould proceeds in consecutive stages, and that citric acid is 

 one of the earliest intermediate products. Currie further proved that, 

 by an appropriate choice of environmental conditions, the metabolism 

 of Asp. niger can be so guided that citric acid production is enhanced, 

 while the further oxidation of this product to oxalic acid and carbon 

 dioxide is inhibited. Thus he was able to increase the citric acid pro- 

 duction from sugar to 50 per cent, whereas under the conditions com- 

 monly employed never more than trace amounts of this substance are 

 found. 



Here is another example. Pasteur already knew that during a nor- 

 mal alcoholic fermentation a small quantity of glycerol, ordinarily 

 about 2-3 per cent of the fermented sugar, is formed in addition to 

 the major products, alcohol and carbon dioxide. When during the 

 war Germany suffered from a serious shortage of glycerol, owing to 

 the deficit of fats, various investigators raised the question whether it 

 might not be possible under special conditions to induce the yeast to 

 an increased glycerol production. Probably fully independently, this 

 problem was simultaneously solved by Connstein and Liidecke, and 

 by Neuberg and collaborators in Germany, by Schweizer in Switzer- 

 land, and, later, by Eoff and co-workers in the U.S.A. All four groups 

 found that the yield of glycerol can be increased to 25-30 per cent of 

 the sugar by adding appreciable amounts of sodium sulphite to the 

 normal, sugar-containing media. In Germany this process has been 

 used on a large scale. 



What makes this discovery particularly interesting is the fact that 

 Neuberg observed that besides glycerol only very little alcohol was 

 formed, while a large amount of acetaldehyde, equivalent to that of 

 glycerol, was recovered. I cannot here enter into a discussion of the 

 enormous significance that this discovery has exerted on our inter- 

 pretation of the chemical conversions that take place during a normal 



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