FERMAT. 544 FERMENTATION. pies of probabilities. For further information concerning the life and work of Fermat, consult: Libri. Journal des savants (1839, pp. 539-561) : Brassinne. Precis des asuvres mathematiques de Fermat (Paris. 1853) ; Hoefer, in the Nouvelle dverselle, xvii.. 438-51; Henry. "Recherches sur les manuscrits de Pierre do Fermat." in the Bulletin, Boncompagni, vols. xii. and xiii.; Paul Tannery, "Sur la date des prin- cipale- decouvertes de Fermat." in the Hull- tin Darboux, 2d series, vol. vii. (1883); and '"Lea manuscrits de Fermat," in the Annates de la Faculty des lettres de Bordeaux. The (Euvres of Fermat were republished by Tannery and Henry under the auspices of the Minister of Public Instruction (Paris, 1891-94). FERMAT A. fer-ma'ta (It., stopped). In music, tin- name given to a pause or resting- point, generally marked by the sign^ . The notes over which this sign is placed are prolonged be- yond their true length. FERMENTATION (from Lat. fermentare, to ferment, from fermentum, yeast, from fervere, to boil). A term applied to the decomposition of certain carbon compounds by the action of living organisms, either directly or by means of enzymes which they secrete. When the sub- stances decomposed contain nitrogen and sulphur (e.g. proteids), ill-smelling gases may be evolved. Such fermentations are usually distinguished as putrefaction. A great variety of carbon com- pounds are fermentable, but carbohydrates and proteids are most notably so. The term was first applied to the decomposition of dissolved sugars into alcohol and carbon dioxide, the latter rising in bubbles through the liquid: the production of gases, though characteristic, is not, however, es- sential to fermentation. Fermentations are often named from the prin- cipal product, e.g. alcoholic, lactic, butyric, acet- ic, etc. The products of fermentations are very numerous and diverse. From carbohydrates are derived various alcohols (ethyl, propyl, butyl, and amyl alcohol, mannite, glycerin I and organic acids (butyric, lactic, acetic, propionic, oxalic. citric, succinic, valerianic, formic, carbonic). From proteids arise ammonia, amido-acids, leu- cin, tyrosin, skatol, and aromatic substances, mercaptans, hydrogen sulphide, marsh gas. car- bon monoxide, nitrogen, hydrogen, etc. Not all of these substances are produced by any one fermentation or from any one substance; indeed, the products vary from time to lime in the course of fermentation, since the substances already formed, or the partial exhaustion of fermentable substances of a certain kind, affect the process. The protoplasm of all plants i- capable of i i He fermentation. In the higher form's, how- ever, this power is confined ordinarily to diges- tive processes, but extraordinary changes occur when i lie plant i- deprived of oxygen for respira- tion, 'lien the protoplasm seems capable of de- po ing ii elf mill thus setting free energy sufficient to tide over the period of oxygen-starva- provided this does not last more than a few hours. This prt -- has been inaptly called in- ilar respiration. Noteworthj alcoholic fcr niaiion ensues when the protoplasm of ripening fruits and seeds and the dying tissues
- t find ei ushed planl - are deprn ed ol oj j gen,
ma] in" of ensilng It has latelj in en shown that fermentation is in these cases often due to an enzyme, zymase, secreted by the proto- plasm. The most active fermentations are pro- duced by the simpler organisms, the bacteria (q.v.) and the lower forms of fungi (q.v.), espe- cially the yeasts and mucors. The fermenting power of these organisms is so conspicuous that they were formerly called 'organized ferments' to distinguish them from enzymes. But the causes of the fermenting power of these lower plants are really the same as those above described for the higher plants, though in the latter it is less striking, because the conditions for its exercise occur more rarely. Some of the ferment organisms are adapted to live wholly without oxygen for respira- tion, securing the necessary energy by fermenting the medium in which they live; such, for example, are the butyric ferments (Bacillus amylobacter) . Others are able to utilize free oxygen, during periods of sluggish fermentation, or to do with-" out it by setting up active fermentation; such are the yeasts. Fermentations may be grouped as (1) split- tin.:: (2) oxidative; (3) compound. ( 1 l Splitting fermentations are most common ; they consist in the separation of the fermentable substance into two or more products. The best- known of these is the alcoholic fermentation of sugar, produced chiefly by yeasts (Saceharo- myces) and mucors. In this process, which is employed commercially on a large scale in the manufacture of beer, wine, and spirits, and in the making of bread, most of the sugar (95 per cent.) is split up into alcohol and carbon dioxide thus: CHeO. = 2C.H,OH + 2CO„. The other 5 per cent, is differently fermented, the products being glycerin, succinic acid. etc. It has been recently shown that this action is due to zymase, an enzyme formed by the yeast, in which several others had previously been found. Only sugars, the number of carbon atoms in whose molecules is 3 or a multiple of 3, can be fermented in this way. Of the hexoses only four, and those dextro- rotatory, are fermentable. Cane-sugar, a disac- charide, is first broken up by invertase into glu- cose and fructose, which are then fermented. Different yeasts attack the sugars differently; some ferment maltose and not saccharose; some ferment fructose better than glucose, others act on it less readily. Alcoholic fermentation is stopped by the accumulation of alcohol in the fluid; 12 per cent, retards and 14 per cent, stops action. Luetic acid fermentation is well known from causing the 'souring' of milk and fruit- juices. Sauerkraut and ensilage depend for their acidity upon it. Lactic acid bacteria (especially the Bacterium acidi-lactici) arc the agents. They attack the glucose directly, and the saccharose and lactose after 'inversion.' converting the former into glucose and fructose and the latter into glucose and galactose. About S3 percent, of the sugar i- converted into ethylidene lactic acid in its three isomeric forms; the rest is transformed into various by-products. The presence of s per cent., or even less, of free acid stops tin' ferments tion. Butyric fermentation is responsible for the aroma of butter. The products (among which are butyric acid) are numerous and diverse; the process i~ complex and varied in its details. (2) Oxidative fermentations cause the forma tioti of in., compounds b oxidation of the eld.
