CH{3}·C·NH ║ ╲ ║ CH, ║ ╱╱ CH·N a substance which is a derivative of methylglyoxal. The idea suggested by Pinkus that acetol is the first product of the action of alkalis on sugar has been rendered very improbable by the experiments of Nef, and the prevailing view (Nef, Windaus and Knoop, Buchner and Meisenheimer) is that the first product is glyceraldehyde, which then passes into methylglyoxal, and finally into lactic acid:-- (1) C{6}H{12}O{6} = 2CH{2}(OH)·CH(OH)·CHO. (2) CH{2}(OH)·CH(OH)·CHO = CH{3}·CO·CHO + H{2}O. (3) CH{3}·CO·CHO + H{2}O = CH{3}·CH(OH)·COOH. All these changes may occur at ordinary temperatures in the presence of a catalyst, and in so far resemble the processes of fermentation by yeasts and bacteria. The first attempt to suggest a scheme of chemical reactions by which the changes brought about by living organisms might be effected was made in 1870 by Baeyer [1870], who pointed out that these decompositions might be produced by the successive removal and re-addition of the elements of water. The result of this would be to cause an accumulation of oxygen atoms towards the centre of the chain of six carbon atoms, which, in accordance with general experience, would render the chain more easily broken. Baeyer formulated the changes characteristic of the alcoholic and lactic fermentations as follows, the intermediate stages being derived from the hydrated aldehyde formula of glucose by the successive removal and addition of the elements of water: [p100] I. II. III. IV. V. CH{2}·OH CH{2}...OH CH{3} CH{3} CH{3} │ │ │ │ │ CH·OH COH..H CH·OH CH(OH) CH{2} │ │ │ │ ╱ CH·OH C..OH..H C(OH){2} CO O │ │ │ ╱ ╲ CH·OH COH...H C(OH){2} O CO │ │ │ ╲ ╱ CH·OH COH...H C(OH){2} CO O │ │ │ │ ╲ CH(OH){2} CH...(OH){2} CH{3} CH(OH) CO │ ╱ CH{3} O ╲ CH{2} │ CH{3} The immediate precursor of alcohol and carbon dioxide is here seen to be the anhydride of ethoxycarboxylic acid (V), whilst that of lactic acid is lactic anhydride (IV). (Baeyer does not appear, as recently stated by Meisenheimer [1907, p. 8], Wohl [1907, 2], and Buchner and Meisenheimer [1909] to have suggested that lactic acid was an intermediate product in alcoholic fermentation, but rather to have represented independently the course of the two different kinds of fermentation, the alcoholic and the lactic.)