LECTURE XX. 



f 



FERMENTS. 1 



WE have repeatedly encountered the conception ferment in our discussion 

 of the transformations of our organic foodstuffs in the alimentary tract and 

 in the tissues. We have seen that the proteins are subjected to the action 

 of pepsin-hydrochloric acid in the stomach, and to trypsin in the intestine, 

 and that the ferment diastase decomposes almost completely the compli- 

 cated carbohydrates in the mouth, and to a much greater extent in the 

 intestine, while the ferment lipase hydrolyzes the fats in the stomach and 

 in the intestine. The ferments also participate largely in tissue-metabolism. 

 We meet them wherever life processes occur. They are distributed as 

 widely in the vegetable world as in the animal kingdom. Fermentation 

 phenomena are so striking that they were recognized in very early times, 

 alcoholic fermentation first attracting attention. Spallanzani, 2 in 1785, 

 showed the solvent action of the gastric juice on protein, while Kirchhoff, 3 

 a few years later, called attention to the fact that fresh gluten will saccharify 

 starch. Liebig and Wohler 4 discovered emulsin, which splits amygdalin, 

 and Bussy identified myrosin. If to these we add the discovery of the 

 oxidases by Schonbein, and the preparation by Berthelot of yeast invertin, 

 the action of which upon cane-sugar was known even to Mitscherlich, we 

 shall include practically all of the most important fermentation phenomena 

 known at the end of the nineteenth century. It is only during the last 

 few decades that we have really made any great progress in our knowledge 

 concerning the various kinds of ferments. 



Before discussing the nature of the ferments and their action, we must 

 state in advance that we have not yet succeeded in characterizing the 

 ferments as chemical individuals. We know practically nothing concern- 



1 In order to avoid confusion, we shall employ the term "ferment" in its original sense, 

 something which causes fermentation. It has been customary to distinguish between 

 organized ferments and unorganized ferments, or enzymes; but it will be shown in the 

 following pages that such a distinction was based upon a misapprehension. For a more 

 complete orientation concerning ferments and fermentations, consult J. Reynolds 

 Green: The Enzymes; and Carl Oppenheimer: Die Fermente und ihre Wirkungen, 

 Leipzig, 1903. 



2 Lazz. Spallanzani: Versuche uber d. Verdauungsgeschaft. Leipzig (1785). 



3 Schweiger's Journal, 14, 389 (1815). Dubrunfaut: Soc. Agricult. Paris (1823.) 



4 Poggendorff's Ann. 41, 345 (1837). 



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