CHANGES IN EXPRESSED YEAST JUICE. 467 



juice, it becomes active once again (its power being increased 

 threefold, or even more). 



According to BUCHNER and RAPP (VI.), centrifugalising the 

 expressed juice effects no change in its fermentative power, the 

 various layers of the juice being of equal power before and after 

 the treatment, provided the temperature has been kept within 

 normal limits during the operation. 



Alcoholic fermentation is an exothermic process, the decom- 

 position of sugar into alcohol and carbon dioxide being accom- 

 panied by a greater disengagement than is observed during 

 the action of other enzymes. This subject has been dealt with 

 by FITZ (XII.), BERTHELOT (VII.), BOUFFARD (II.), BROWN (VIII.) 

 and RUBNER (III. and IV.). Whereas Brown and Berthelot 

 merely calculate that the heat liberated in the formation of the 

 alcohol and carbon dioxide exceeds that requisite for the splitting 

 up of the dextrose, and give the heat value as 67 and 33 calories 

 respectively, Fitz, on the other hand, established by direct 

 experiment that the temperature of an 18 per cent, solution of 

 sugar increased by 18 C. during fermentation, but that 6 C. of 

 this increase was due to a positive increment of heat external to 

 the actual process of fermentation. The same thing was clearly 

 shown in a primitive experiment by E. BUCHNER (X.), and 

 Bouffard determined the heat of fei mentation in a litre of grape 

 must as 23.5 calories. Brown, in repeating this experiment with 

 malt wort, found the heat of fermentation to be 119.2 cal. per 

 gramme of maltose, or 21.4 cal. when referred to the gramme- 

 molecule for comparison with Bouffard's figures. Finally, Rubner 

 worked out accurate methods of determination, and recommended, 

 in the first place, a differential method for estimating the heat of 

 combustion of a nutrient medium before and after the growth of 

 germs, and, secondly, a direct method of determining the heat 

 liberated during the continuance of the vital activity. He 

 determined the heat of combustion of bottom yeast as 4475 

 gramme-calories per grm. of dry substance, and that of top yeast 

 as 4554 gramme-calories. Further experiments with alcoholic 

 fermentation gave the mean value 149.5 gramme-calories (12 

 tests) as the heat of fermentation per grm. of saccharose. 



In all cases the action of the enzyme is dependent, in a high 

 degree, on the chemical reaction of the test liquid. According to 

 BUCHNER and RAPP (I. and II.), the fermentative action of 

 expressed yeast juice is accelerated by an addition of small quan- 

 tities of alkalis, such as potassium carbonate, disodium phosphate 

 and alkali arsenites. WHOBLEWSKI (III.) and also HARDEN and 

 YOUNG (III.) have expressed themselves in a similar sense, the first- 

 named attributing considerable importance to phosphates, both 

 alone and in presence of acids or alkalis. According to the first- 

 named worker (I.), an addition of 0.05 per cent, of hydrochloric 

 acid or acetic acid is injurious to the fermentative action (see also 



