On Expressed Yeast-cell Plasma (fitichners " Zymase "). 251 



These further investigations, Buchner considers, are confirmatory of 

 the conclusion drawn by him from his original experiments, viz., that 

 the activity of the yeast-cell as an alcoholic ferment depends upon the 

 action of a soluble enzyme of an albuminoid character elaborated by 

 the living cell. To this soluble ferment Buchner applies the 

 name " Zymase." 



The subject presented so many phases not only of special but also 

 of general biological interest that we were led to pursue its investiga- 

 tion. We considered this the more necessary since Buchner's experi- 

 ments were carried out entirely with bottom-fermentation yeasts, and 

 it appeared of interest to ascertain whether top-fermentation yeasts 

 (as used in English brewing) give parallel results. At the outset we 

 carefully adhered to Buchner's method of expressing the cell plasma ; 

 but owing to the tediousness of the process we were led, after many 

 attempts, to adopt the following arrangement for the extraction of the 

 cell plasma or juice. 



Method of Preparation of the Cell Plasma. The yeast as received 

 from the brewery is a thick, pasty, frothy mass, consisting of yeast- 

 cells intermixed with more or less fermented wort. For the purpose 

 in view it is necessary to separate the yeast-cells from all adherent 

 matter which would by its presence influence the composition of the 

 expressed juices. The purification of the yeast is thus a necessary 

 preliminary operation, and is accomplished as follows : 



To the pasty mass of crude yeast is added an equal part of water 

 and the mixture stirred together. This suspension of yeast-cells is 

 then centrifugalised, whereby the contained cells are separated as a 

 thick creamy mass at the bottom of the containing vessel. The super- 

 natant liquor is decanted and the mass of cells again stirred into a 

 suspension in a fresh quantity of water. The mixture is again centri- 

 fugalised, and the process repeated until the last added water comes 

 away clear and colourless. The final product of this process is a firm 

 mass of yeast-cells closely packed together, with a minimal quantity of 

 adherent water. It is necessary to remove even this quantity of 

 water if a natural juice is to be obtained. The pasty mass of yeast is 

 wrapped in a double thickness of " hydraulic chain cloth " and intro- 

 duced into one of a series of shallow iron trays, so constructed that the 

 pile can be strongly compressed in a hydraulic press and the expressed 

 liquor run off. In this process, which is a modified form of filter- 

 pressing, the last adherent portions of water are removed from the 

 yeast-cell, and the mass of yeast as removed from the cloths appears as 

 a perfectly dry white powder, consisting of yeast-cells with approxi- 

 mately dry exteriors. The pressure necessary to produce this result is 

 from 70 100 atmospheres. 



The disintegration of the yeast-cell is the next process. This is 

 accomplished by a mechanical contrivance which maintains the yeast, 



