12 Scientific Proceedings, Royal Dublin Society. 



Such a lessening of pressure is under ordinary circumstances made good by 

 the diffusion 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 decreasing viscosity of the sap owing to 

 sugars having been used up, yet, quantitatively considered, this explanation 

 seems insufiicient, 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 ionised ammonium salt have been shown by 

 Ehrlich (4) 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. 



Bibliography. 



1. Dixon, H. H., and Atkins, W. R. G. : On Osmotic Pressure in Plants : 

 and on a Thermo-Electric method of determining Freezing-points. 

 Sclent. Proc. Roy. Dubl. Soc, vol. xii(N.S.), 1910, 275. 



2. Osmotic Pressures in Plants II. — Oryoscopic and Conduc- 



tivity Measurements on some Vegetable Saps. Seient. Proe. Roy. 

 Dubl. Soc, vol. xiii (N.S.), 1913, p. 434. 



The Extraction of Zymase by Means of Liquid Air. 



Sclent. Proc. Roy. Dubl. Soc, vol. xiv (N.S.), 1913, p. 1. 



Ehrlich, F. : Ueber die Entstehung der Bernsteinsaure bei der alko- 

 holischen Qarung. Biochem. Zeitschr., 1909, Bd. xviii, s. 391. 



Paine, S. G-. : The Permeability of the Yeast-Oell. Proc. Roy. Soc, 

 Ser. B., vol. Ixxxiv, 1911, p. 289. 



