454 Messrs. Harden and Paine. Action of Dissolved [Oct. 17, 



substance which would produce no plasmolysis of yeast even in concentrated 

 solution, and to show that it would not cause acceleration. In earlier 

 experiments urea was found to produce no plasmolysis at molar concentra- 

 tion. The determination of the effect of this substance upon the rate of 

 autofermentation was therefore of first importance. In one experiment molar 

 urea was compared with molar sodium chloride and water. The urea was 

 found to be without influence, as shown in the curves (p. 453). 



In the following experiment (No. 85) the effects of isotonic solutions of 

 urea, sodium chloride, and potassium nitrate were compared. 



Table VIII.— Effect of Urea Solutions. 



No. 85 



10 grm. yeast + 20 c.c. solution. 







NaCl 



Urea 



KN0 3 



Urea 



Water 





5 -85 grm. 

 100 c.c. 



9 -0 grm. 

 100 c.c. 



5 '05 grm. 



100 c.c. 

 = '5 molar 



4-5 

 100 c.c. 







Depression of freezing 







1-46° 



1-42° 





Time. 



Cubic centimetres of carbon dioxide. 



o-o 



0- 5 



1 -o 



1- 5 



34-0 

 65 -0 

 86 -5 



17 -0 

 29 -2 

 34 -5 



21 -3 

 46 -7 

 60 "3 



16 -5 

 29 -4 

 35 -5 



17 -0 



29 -3 

 35 -5 



Urea is thus seen to be without influence upon the rate of auto- 

 fermentation, although, as shown by the depression of the freezing-point, the 

 solutions of this substance were isotonic with the corresponding salt controls. 

 The fact that plasmolysis of the cells is not produced by urea solutions 

 would seem to indicate that this substance can penetrate freely through the 

 cytoplasm of the yeast cell. An experiment was made to investigate this 

 point, the method described by Paine (2) being employed ; 100 grm. of 

 yeast were suspended in 100 grm. of molar urea solution, allowed to stand 

 20 hours at a temperature approximating to zero, and the distribution of 

 urea determined (Table IX). 



Urea is thus seen to penetrate readily into the cells, the factor K 

 representing the coefficient of diffusion being of the same order as that 

 obtained for alcohol, namely, - 85 to - 87. Although urea enters the cells it 

 is without influence upon the rate of autofermentation. 



