The reaction is produced by all races of brewer's yeast which have been tried, as well as by active yeast preparations and extracts and by wine yeasts [Neuberg and Karczag, 1911, 4; Neuberg and Kerb, 1912, 2]. The phenomenon can readily be exhibited as a lecture experiment by shaking up 2 g. of pressed yeast with 12 c.c. of 1 per cent. pyruvic acid, placing the mixture in a Schrötter's fermentation tube, closing the open limb by means of a rubber stopper carrying a long glass tube and plunging the whole in water of 38-40°. Comparison tubes of yeast and water and yeast and 1 per cent. glucose may be started at the same time, and it is then seen that glucose and pyruvic acid are fermented at approximately the same rate [Neuberg and Karczag, 1911, 1]. If English top yeast be used it is well to take 0·5 per cent. pyruvic acid solution and to saturate the liquids with carbon dioxide before commencing the experiment. The production of acetaldehyde can be readily demonstrated by distilling the mixture at the close of fermentation and testing for the aldehyde either by Rimini's reaction (a blue coloration with diethylamine and sodium nitroprusside) or by means of p-nitrophenylhydrazine which precipitates the hydrazone, melting at 128·5° [Neuberg and Karczag, 1911, 2, 3]. [p082] As the result of quantitative experiments it has been shown that 80 per cent. of the theoretical amount of acetaldehyde can be recovered. The salts of the acids are also attacked, the carbonate of the metal, which may be strongly alkaline, being formed. Thus taking the case of pyruvic acid, the salts are decomposed according to the following equation:-- 2CH{3}·CO·COOK + H{2}O = 2CH{3}·CHO + K{2}CO{3} + CO{2}. Under these conditions a considerable portion of the aldehyde undergoes condensation to aldol [Neuberg, 1912]:-- 2CH{3}·CHO = CH{3}·CH(OH)·CH{2}·CHO. This change appears to be due entirely to the alkali and not to an enzyme since the aldol obtained yields inactive β-hydroxybutyric acid on oxidation [Neuberg and Karczag, 1911, 3; Neuberg, 1912]. The various preparations derived from yeast which are capable of producing alcoholic fermentation also effect the decomposition of pyruvic acid in the same manner as living yeast. They are, however, more sensitive to the acidity of the pyruvic acid, and it is therefore advisable to employ a salt of the acid in presence of excess of a weak acid, such as boric or arsenious acid, which decomposes the carbonate formed but has no inhibiting action on the enzyme [Harden, 1913; Neuberg and Rosenthal, 1913].