TRANSACTIONS OF SECTION B. 67^ 



Evidence was brought forward to show that the initial rate of fermentation by- 

 living yeast is controlled almost completely by one single reaction. By consider- 

 ing only these initial velocities certain disturbing secondary reactions are elimi- 

 nated, for change of conditions, which are usually considered to influence the 

 rate of fermentation, have no effect on these initial velocities. The simple laws 

 governing the rate are evidence in favour of considering one reaction to have the 

 control of the velocity. 



The rate of fermentation is exactly proportional to the amount of yeast 

 present. The rate of fermentation of the four fermentable hexnses (glucose, 

 fructose, galactose, and mannose) is almost independent of the concentration of 

 the sugar. Glucose and fructose are fermented at approximately equal rates. 

 Yeasts which ferment glucose do not always possess the property of fermenting 

 galactose, and this sugar is fermented only by yeasts which have been grown 

 in the presence of galactose. The fermentation of mannose is similar to that of 

 glucose, but the rates of the two reactions a j not equal. The enzyme which 

 ferments m^innose seems to be move sensitive to heat than the one which ferments 

 glucose. The influence of temperature on these rt-actions is almost the same in 

 the case of glucose, fructose, and mannose, but rather less in the case of galactose. 

 These results are most easily brought into accord on the assumption that the 

 enzyme combines with the sugar. Glucose and fructose form the same compound ; 

 galacto.se and mannose form different compounds. It is possible that there exist 

 three difl'erent enzymes: glucozymase, which ferments glucose and fructose; galac- 

 tozymase, which ferments galactose ; and mannozymase, which ferments mannose. 

 It is probable that no compound has yet been isolated which can be considered 

 intermediate in alcoholic fermentation. The suggestion that lactic acid is such a 

 compound is of special interest, and has attracted much attention. Lactic acid 

 does not ferment, or ferments only very slowly and incompletely. This is the 

 chief objection to the hypothesis. An intermediate compound must be at least as 

 reactive as the original reagent. The suggestion that lactic acid is liberated in a 

 ' nascent state' is considered unlikely, for in constructing the mechanism of other 

 similar chemical reactions such suppositions have not been found necessary. 



Fermentation by yeast-juice differs in many respects from that by living yeast. 

 It is probable that the mechanism of the reaction is the same in each case ; 

 but the relative rates of tlie different steps in the two processes are different. The 

 experiments show that there is an essential step in fermentation in which phos- 

 phates in some form or another play a part. This reaction proceeds too 

 rapidly in fermentation by living yeast to have any controlling influence on the 

 velocity; but in the fermentation by yeast-juice it proceeds relatively more slowly 

 and influences the rate. 



The method of investigating complicated reactions by considering onlv initial 

 velocities has the advantage that disturbing side reactions are to a large" extent 

 eliminated. The method can probably be applied with advantage to other 

 enzyme processes. 



2. Hue Selective Pervieahility of certain Seeds. 

 By Professor Adrian Brown. 



3. The Production of Ammonia from Atmospheric Nitrogen by vieans 

 of Peat. By H. C. Woltereck, Ph.D. 



Attempts to utili.se the nitrogen contents of peat have been made durino- the 

 last sixty years, but the yield of ammonia obtained by the various processes which 

 have been tried ghows that only about one-third of the nitrogen can be thus 

 recovered. Starting from an observation that a mixture of nitrogen and hydroo-en 

 passed over reduced iron at a low beat always produced ammonia for some time, 



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