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The Permeability of the Yeast-Cell. 



By Sydney G. Paine, Research Scholar in the Biochemical Department, 

 Lister Institute, London. 



(Communicated by Arthur Harden, F.R.S. Received July 12, 1911.) 



The question of the permeability of plant membranes and of the proto- 

 plasm lining plant cells has received just attention from time to time, the 

 method usually employed being based upon plasmolysis, a phenomenon 

 first described by Nageli in 1855 (1), and subsequently investigated by 

 Pfeffer (2), De Vries (3), and Overton (4). The results of their experiments tend 

 to show that purely physical diffusion laws cannot always interpret osmotic 

 phenomena as exhibited by living plant cells, but that in some cases there is 

 evidence of specific permeability. 



Nathanson (6) finds that the permeability of protoplasm for any substance is 

 not constant, but varies according to the concentration within and without 

 the cells, and he holds that these variations cannot be accounted for in a 

 purely physical manner. 



In 1899 Overton (5), in a series of very comprehensive investigations, 

 observed the similarity existing between solutions in oils and in the 

 ectoplasmic layer of the cytoplasm; he showed especially that many 

 substances could be made to enter the plasma by dissolving them in oils, 

 and suggested the hypothesis that the absorption of such substances by 

 living plants might be due to the presence of lecithin and cholesterol in the 

 plasmatic layer. This hypothesis, however, does not account for the semi- 

 permeability exhibited by various plant membranes towards inorganic salts. 

 Again Adrian Brown (7) has shown that the seed coat of Hordcum vulgar c 

 exhibits a remarkable degree of impenetrability to strong acids and to 

 metallic salts, while it admits of ready diffusion of such substances as 

 alcohol, aldehyde, acetone, iodine, and certain salts of mercury and cadmium. 

 Armstrong (8) has attempted to explain these results on the theory of 

 " hormones," but it appears to the author that strong support to Overton's 

 hypothesis is afforded by these experiments of Adrian Brown. It has been 

 shown by Overton that iodine and mercuric chloride, as well as the above- 

 mentioned organic substances, are readily soluble in cholesterol. Since these 

 include most of the substances which were found by Brown to be capable of 

 entering the barley grain, it seemed advisable to ascertain whether the 

 remaining substances found by him to enter the seed, namely, cadmium 

 iodide and trichloracetic acid, also possessed this property of solubility 



