A manual of bacteriology, clinical and applied / by Richard T. Hewlett.

  • Hewlett, R. Tanner (Richard Tanner), 1865-1940.
Date:
1902
Catalogue details

Licence: Public Domain Mark

Credit: A manual of bacteriology, clinical and applied / by Richard T. Hewlett. Source: Wellcome Collection.

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    faction of gelatin is due to an enzyme, and if a little of the liquefied gelatin free from organisms be added to fresh solid gelatin it will produce liquefaction of this, and the same occurs in the presenceof chloroform, which inhibits bacterial action. Yeast also secretes enzymes ; it is unable to directly ferment cane sugar with the production of alcohol, but by the action of the enzyme ‘ invertin ’ the cane sugar becomes inverted, i.e. the molecule is split up into dextrose and Isevulose, which are then further acted upon with the production of alcohol. The following are the chief varieties of fermentation : The Alcoholic Fermentation.—This is mainly brought about by the decomposition of sugars of the glucose group (C6H1206)„ by yeasts into alcohol and carbonic acid, but some of the bacteria and moulds also produce appreciable quan¬ tities of alcohol. It is not necessary, however, that glucose should be present, for other carbohydrates by the action of enzymes secreted by the organisms are converted into glucose, which is then fermented. The general reaction is as follows : C6H, 206 = 2C2H60 + 2C02. As a matter of fact a small amount of by-products appears in addition to the alcohol and carbonic acid, viz. glycerin, succinic acid, and higher alcohols. Until lately no enzyme had been obtained which would carry out this change; it only occurred when the living yeast-cells were present. Recently, Buchner has claimed to have separated an enzyme from yeast cells, which will decompose glucose with the formation of alcohol. Macfadyen, Morris, and Rowland,1 however, do not accept Buchner’s conclusions, and the question must be regarded as not yet decided. The Lactic Acid Fermentation.—This is brought about chiefly by bacteria. Glucoses are converted into lactic acid, the reaction being : Cf)H 120,=2 (HC3H503), 1 Proc. Roy. Soc. Lond. 1900.