1911.] 



The Permeability of the Yeast-Cell. 



In the experiments with cadmium iodide and mercuric chloride con- 

 siderable plasmolysis occurred, but this fact cannot be taken to indicate that 

 no diffusion of these substances had taken place, since a marked change was 

 observed in the appearance of the yeast. The cells became much paler in 

 colour and more opaque, while the liquid assumed a dark brownish-grey 

 colour. From the solid appearance of the cells, it would seem that these 

 salts had penetrated through the membrane and coagulated and contracted 

 the cytoplasm ; this appears the more evident in the case of the relatively 

 weaker solution of mercuric chloride, where plasmolysis went on slowly up 

 to the end of three hours, after which a strong and rapid contraction took 

 place. These facts are explicable on the assumption that the proteins of the 

 ectoplasm are slowly coagulated during the first three hours and by con- 

 traction leave open access for the solution to the inner layers. 



In another series of experiments 10 grm. of pressed yeast were weighed 

 out into each of several Nessler glasses and treated with 20 c.c. of the 

 solutions tabulated below. The tubes were allowed to stand in ice water 

 during about 20 hours. They were then centrifuged in batches of four, 

 each batch being spun for exactly 21 minutes. The tubes were then 

 weighed, the liquids poured off into measuring vessels and the weights of the 

 residues ascertained by re-weighing the tubes. 



No plasmolysis was produced by solutions of acetone, urea and the lower 

 concentrations of alcohol up to 10 per cent. With the higher concentrations 



Table III. 



Percentage Volume of 

 of | liquid 



poured off. 



25 



Acetone, molar 



Urea, molar 



Glycerine, molar 



Sulphuric acid, \ molar 



Acetic acid, molar 



Sodium chloride, molar 



„ molar 



Sodium acetate, molar 



Sodium sulphate, £ molar 



Magnesium sulphate, molar 



„ T \j molar.. 



Sodium phosphate, T % mo lar 



Sodium arsenate, f 3 molar 



