90 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



inwards of sugar from the wort, hence this carbohydrate 

 must be able to pass freely into the cell, while the alcohol 

 produced passes out, maintaining a constant ratio, as 

 shown by Paine (loc. cit.). A well-marked but relatively 

 small extra fall in pressure was observed in No. 611, where 

 the yeast, after separation from the beer, was suspended 

 in a linen cloth in a large vessel of water with a delivery 

 tap and overflow. 



The small degree of permeability of the yeast as regards 

 electrolytes is clearly brought out by the conductivity of 

 the juice being from four to five times that of the beer. 

 Even allowing for fluctuations from sample to sample, 

 there is a well-marked rise in conductivity in yeast after 

 its separation. While this may be due in part to decreas- 

 ing viscosity of the sap owing to sugars having been used 

 up, yet, quantitatively considered, this explanation seems 

 insufficient, and Nos. 610 and 611 make it more probable 

 that such a result is partly due to the retention of an acid 

 produced in fermentation, which in the normal course 

 would diffuse very slowly outwards. Succinic acid, for 

 instance, and its more highly ionized ammonium salt have 

 been shown by Ehrlich (1909) to arise during fermentation 

 from glutamic acid. 



To avoid the possibility of error in the comparison of 

 yeast- juice and beer owing to the expulsion of gases by 

 freezing the former solid, measurements were made of both 

 freezing-point and conductivity of beer as separated from 

 yeast and after freezing solid. No appreciable difference 

 was observed between the two sets of figures. 



2. RESEARCHES BY THE METHOD OF PLASMOLYSIS. The 

 plasmolysis of the yeast cell has lately been investigated 

 by Euler and Palm (1914), using solutions of glycerol. It 

 had previously been showTi by Bokorny (1903) that yeast 

 retains its fermentative power in solutions of sugars which 



