BUCHNER'S ZYMASE OR ALCOHOLASE. 475 



contains very little zymase, if any." According to LANGE (II.) 

 the alcoholase content is dependent to some extent on the nitrogen 

 content (seep. 259, vol. ii.), which latter is stated by HAYDUCK (V.) 

 to be a measure of the fermentative power of the yeast. GREEN 

 (III.) also found that the formation of alcoholase is an inter- 

 mittent function ; and this view is confirmed by the results of 

 the different workers who obtained expressed yeast juice with 

 little or no fermentative power. The behaviour of yeast that 

 will no longer excite normal fermentation in beer wort after being 

 used a certain number of times is also attributable to this cause. 

 All these facts clearly indicate that the alcoholase content, and 

 therefore the fermentative power, of yeast necessarily vary with 

 the age of the yeast and divers other circumstances as well as 

 with the character of the organism. This is a point that should 

 be borne in mind in further investigations, the more readily so 

 because the preparation of acetonised permanent yeast has 

 afforded us a reliable means of arresting and determining at any 

 stage all the reactions proceeding in the cell. 



The alcoholase content of yeast during storage at low tem- 

 peratures, under ice water, and in the regenerative process, has 

 been traced in this way. The present is a most appropriate 

 moment for devoting closer attention to the regenerative process 

 of HAYDUCK (VI.). Previous to the time of that worker, 

 brewers had frequently noticed that yeast after repeated use 

 gradually ceased to give a satisfactory " break " (see p. 187, vol. ii.) 

 and furnished a less compact sedimental yeast (see p. 2 31, vol. ii.). 

 HAYDUCK (V.), uninfluenced by E. 0, Hansen's recent discovery 

 of the existence of a multiplicity of yeast species, many of them 

 capable of causing haze in beer, attributed one cause of yeast 

 degeneration (see p. 268, vol. ii.) to a surfeit of nitrogenous food 

 (p. 215, vol. ii.), having traced, by analysis, the growing nitrogen 

 content in the dry residue during the repeated employment of the 

 yeast in brewing practice. In 1884 he attempted to lessen this 

 injurious surplus by allowing the yeast to develop in a vigorously 

 aerated wort at a higher temperature than that of the fermentation 

 room, though not so high as to check reproduction. Then, stimu- 

 lated by the favourable results obtained independently by a brewer, 

 whose name has not transpired, HAYDUCK (VI.) replaced wort 

 by a boiled solution of sugar (hopped in order to suppress 

 bacteria) which, when vigorously aerated, gave a yeast crop 

 comparatively poorer in nitrogen. In the present more complete 

 state of knowledge respecting the nature of fermentation dis- 

 turbances, there is no need to labour the point that this treatment 

 might occasionally increase the quantity of any pre-existing 

 disease yeasts in the sample, and certainly could not preclude 

 that possibility. The method did not find any practical applica- 

 tion. Nevertheless, it is worthy of mention, since, though as 

 stated above it might occasionally lead to highly undesirable 



