The fermentation of dihydroxyacetone was moreover proved by Harden and Young [[1912]] to be effected by yeast-juice and maceration extract at a much slower rate than that of the sugars, in spite of the fact that the addition of dihydroxyacetone did not inhibit the sugar fermentation. The same thing has been shown for living yeast by Slator [[1912]] in agreement with the earlier results of Buchner [[1910]] and Buchner and Meisenheimer [[1910]].

The logical conclusion from Lebedeff's experiments would appear rather to be that dihydroxyacetone is slowly condensed to a hexose and that this is then fermented in the normal manner [Harden and Young, [1912]; Buchner and Meisenheimer, [1912]; Kostytscheff, [1912, 2]]. Buchner and Meisenheimer, however, regard this as improbable on the ground that dihydroxyacetone, being symmetric in constitution, would yield an inactive hexose of which only at most 50 per cent. would be fermentable. Against this it may be urged, however, [p107] that enzymic condensation of dihydroxyacetone might very probably occur asymmetrically yielding an active and completely fermentable hexose. Buchner and Meisenheimer, however, still support the view that dihydroxyacetone forms an intermediate stage in the fermentation of glucose and adduce as confirmatory evidence of the probability of such a change the observation of Fernbach [[1910]] that this compound is produced from glucose by a bacillus, Tyrothrix tenuis, which effects the change both when living and after treatment with acetone.

The balance of evidence, however, appears to be in favour of the opinion that dihydroxyacetone does not fulfil the conditions laid down by Slator (see p. [103]) as essential for an intermediate product in the process of fermentation [see also Löb, [1910]].

Lebedeff subsequently [[1912, 4]; Lebedeff and Griaznoff, [1912]] extended his experiments to glyceraldehyde and modified his theory very considerably. Using maceration extract it was found in general agreement with the results of Buchner and Meisenheimer (p. [105]) that 20 c.c. of juice were capable of producing about half the theoretical amount of carbon dioxide from 0·2 gram of glyceraldehyde, whereas 0·4 gram caused coagulation of the extract and a diminished evolution of carbon dioxide. The addition of phosphate diminished rather than increased the fermentation. Even in the most favourable concentration however (0·2 gram per 20 c.c.) the glyceraldehyde is fermented much more slowly than dihydroxyacetone or saccharose, as is shown by the following figures:—

20 c.c.
Extract +
0·2 gram. 		CO2 in grams in successive periods of Duration of fer-
ment-
ation 		Total CO2
6 hours.18 hours.24 hours.
Cane sugar0·0500·0000·0006 0·05
Dihydroxy-
acetone		0·0420·0000·0006 0·042
Glycer-
aldehyde		0·0080·0220·005480·035

Further, during an experiment in which 0·129 gram of CO2 was evolved in 22·5 hours from 0·9 gram of glyceraldehyde in presence of phosphate, no change in free phosphate was observed, whereas in a similar experiment with glucose a loss of about 0·2 gram of P2O5 would have occurred. Hence the fermentation takes place without formation of hexosediphosphate. This was confirmed by the fact that the osazone of hexosephosphoric acid was readily isolated from the products of fermentation of dihydroxyacetone (0·259 gram of CO2 having been evolved in twenty hours) but could not be obtained from those of glyceraldehyde (0·138 gram CO2 in twenty hours). [p108]

This result is extremely interesting, although it is not impossible that the rate of fermentation of the glyceraldehyde is so slow that any phosphoric ester produced is hydrolysed as rapidly as it is formed.

Lebedeff regards the experiments as proof that phosphate takes no part in the fermentation of glyceraldehyde and bases on this conclusion and his other work the following theory of alcoholic fermentation.

1. The sugar is split up into equimolecular proportions of glyceraldehyde and dihydroxyacetone:—

(a) C6H12O6 = C3H6O3 + C3H6O3.