306 



Mr. S. G. Paine. 



[July 12,. 



Summary and Conclusions. 

 The early experiments on plasmolysis of yeast seemed to indicate that the 

 envelope of the yeast-cell was impermeable by inorganic salts generally 

 while it allowed of the ready diffusion of such substances as alcohol, acetone,- 

 and urea, which have been known to pass with ease through many forms of 

 living protoplasm. 



Quantitative estimations have shown the power of diffusion of alcohol to 

 be very different from that of inorganic salts. On immersion of yeast in 

 dilute alcohol, varying from 5 per cent, to 20 per cent., the ratio of the 

 concentration within the cells to that of the liquid outside becomes practically 

 constant, and independent of the absolute concentration. Alcohol is believed 

 to diffuse quite readily into the cell, but at the same time this ratio is not 

 unity, but a constant which deviates only slightly from 0"85. Probably the 

 whole of the water in the cell, which is removed by drying at 98° C, is not 

 available for diffusion of alcohol. The amount of water thus bound up r 

 possibly as a constituent of the protoplasmic complex, appears to vary some- 

 what at different stages in the life-history of the cell, but the method was 

 not considered sufficiently delicate to render further study of this interesting 

 phenomenon advisable in this way. 



All salts which have been tried have been taken up by yeast from 

 moderately concentrated solutions, and in the cases of sodium chloride and 

 ammonium sulphate even from dilute solutions. But, whereas with alcohol the 

 amount entering the yeast during three hours was practically equal to the 

 amount which entered on prolonged immersion, with these salts the process 

 was a slow one. After three hours no sodium chloride had entered from a 

 decimolar solution, and considerably less ammonium sulphate was found in 

 the yeast than was the case after longer standing. From decimolar solution 

 of sodium phosphate no entrance of phosphorus was appreciable even after 

 20 hours' standing, but from more concentrated solution, 0*3 molar, a well 

 marked entrance was observed. Since phosphates are essential for the life 

 of the yeast and are gradually assimilated and accumulated from very dilute 

 solutions, the envelope must admit the necessary amount of these substances 

 required by the cell for its metabolism. The amount thus absorbed during the 

 time of these experiments would naturally be very small and indeterminable. 



With regard to the entrance of salts, which the experiments have shown 

 to occur, the following considerations are of interest. Since the yeast must 

 of necessity be analysed as a whole, the question as to how far into the cells 

 the various substances have penetrated must, at present, remain in doubt. 

 While most salts do show some entrance into the cells, the factor which is 

 taken as an expression of permeability is, except in the case of copper 



