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Schardinger has obtained 1-lactic acid in one instance. It is very probable that the inactive lactic acid is formed first, and is then converted into one of its active varieties, as shown by Frankland and MacGregor in the case of the formation of d-lactic acid.

B-hydroxypropionic acid, CH2OH-CH2-COOH, the isomer of ordinary lactic acid or a-hydroxypropionic acid, was obtained by Hilger, by the fermentation of inosite; it was identified by oxidation to malonic acid. Vohl has repeated this experiment, but he obtained a-hydroxypropionic acid; this acid (generally termed lactic acid of fermentation) is thus always produced in fermentation.

Lactic acid is also a product of the fermentation of certain polyhydric alcohols, e.g. sorbite, inosite, mannite, and dulcite; also of rhamnose (Tate) and other pentoses; it can also be formed by fermentation from malic acid, carbon dioxide being evolved during the process :—

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Wehmer, in 1892, showed that certain monosaccharides, but especially glucose, could undergo yet another change as the result of fermentation, citric acid being the product formed. Two species of micro-organisms were found capable of producing this result, carbon dioxide being evolved during the process. The citric acid obtained is identical with that found in lemon juice, and is the principal product. For this process air is a necessity, the carbon dioxide evolved during the fermentation even hindering the action of these micro-organisms, and consequently it must be allowed to escape. Over 50 per cent. of the glucose can be transformed into citric acid; but if the acidity of the solution reaches 20 per

cent., it becomes deleterious to these micro-organisms, and must be removed by neutralisation, in order that the total quantity can be obtained; if the fermentation is allowed to go too far, the citric acid itself is decomposed. Wehmer has since obtained three other micro-organisms which can produce this fermentation.

Oxalic acid is another product obtained by the fermentation of sugar solutions, which may consist of glucose, galactose, cane sugar, lactose, maltose, dulcitol, mannitol ; glycerol can also be converted into oxalic acid in the same way. The micro-organisms which produce this change are hindered in their action by excess of the acid, and a good yield of oxalic acid is only obtained when it is neutralised as fast as it is formed by calcium carbonate, which can be added to the solution. According to Banning, fifteen species of micro-organisms are now known which can produce oxalic acid, all of them from glucose, and the majority from arabinose; glycerol and erythritol by about half of them, as also pyrotartaric acid and glycollic acid. This investigator gives a list of what substances and by how many of these micro-organisms each of the substances is converted into oxalic acid.

The curious phenomenon, observed in wines and saccharine liquids, known as "ropiness," is the result of a fermentation, and is due, according to Pasteur, to a particular organism. It is observed sometimes in the manufacture of cane sugar, and the result is a peculiar viscosity. The change that occurs is probably caused by two organisms, since Pasteur has observed larger and smaller particles of a different kind in the liquid; one of these produces the peculiar gum which resembles dextrin,

as on oxidation it yields oxalic, not mucic acid, and the other produces mannite. During the process, carbon dioxide is evolved; that the process is in all probability due to two organisms is further seen by the varying quantities of gum and mannite produced, that of the gum being very often much larger. Monoyer has proposed the following equations for these two changes :—

13C12H24012+ 12H2O = 24C6H1406 + 12CO2
12C12H24012

=

12C12H20010+ 24H2O

The gelatinous matter, called by Scheibler dextran, is probably a derivative of cellulose, and it can be formed by several micro-organisms, e.g. Streptococcus hornensis, which produces it from media containing 20 per cent. of glucose (Boekhout). A gum, resembling in properties a galactan, since it yields mucic acid on oxidation, is produced by Bacillus lactis aerogenes in solutions of lactose or galactose, but not glucose (Emmerling).

These changes, which sugar can undergo, are thus very various. Nef has compared the action of enzymes with the action of those reagents which cause the decomposition of methylene compounds, and regards the enzymes as substances exerting a directive influence on the decomposition of the sugars. Very many other theories have. been advanced to explain the processes of the metamorphosis of sugar into alcohol and carbon dioxide, but the suggestion brought forward by Baeyer, in 1870, that water is the active agent, seems to be the most reasonable. He considered that addition of the elements of water took place at certain points, and that by alternate separation and addition in a different order, an accumulation of oxygen atoms at certain parts of the molecule might take

F

place; at these points there would be weakness, and dis

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where the separating elements are indicated by dots.

In 1895 Armstrong drew attention to the fact that accumulation of oxygen atoms might take place at noncontiguous carbon atoms, and he considers that this is a special feature; different effects would thus be produced by different enzymes, since they would affect different systems, and the direction of the attack would depend on the asymmetry of both hydrolyte and hydrolyst. This accounts for the different action of enzymes, as in the case of the glucosides.

CHAPTER VII.

CHANGES RESULTING IN THE FORMATION OF OPTICALLY ACTIVE PRODUCTS.

As has already been pointed out, enzymes and living ferments are very selective in their action upon the carbohydrates and organic acids. Pasteur, in his classical experiments upon the tartrates and racemates, in 18481853, was the first to point out the selective action of micro-organisms. He grew a penicillium upon the ammonium salt of racemic acid, and obtained lævotartaric acid, the dextro- variety being assimilated by the organism.

This method of Pasteur's has been employed in many cases for the separation of optically active compounds; the separation of inactive mandelic acid by Lewkowitsch, in 1882, into its constituents, and the resolution of glyceric acid by Frankland and Frew, in 1891, by the Bacillus ethaceticus, which was grown upon its calcium salts, are two very good examples of this selective action.

Frankland has investigated the action of his Bacillus ethaceticus, and of the pneumococcus of Friedländer, upon several carbohydrates, e.g. maltose, lactose, raffinose, dextrin, mannitol, glycerol, glucose, and arabinose; the chief products were alcohol and acetic acid. Upon

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