1911.] 



The Permeability of the Yeast-Cell. 



291 



The Plasmolysis of Yeast ly Various Substances. 



Preliminary experiments were first made on the degree of plasmolysis of 

 yeast-cells produced, by immersion of the cells in solutions of different 

 substances. For this purpose equal weights of pressed brewer's yeast were 

 intimately mixed with equal volumes of the several solutions and allowed 

 to stand for varying intervals of time. Well-mixed samples were then 

 drawn up into capillary tubes of 10 cm. length, which were afterwards 

 sealed at one end and spun simultaneously in a centrifuge. The columns 

 of residue and of the clear liquid were then measured in millimetres, and 

 from these the ratio of the length of the column of residue to that of the 

 whole column (residue -f liquid) was calculated. 



In all these experiments wort and 7 per cent, alcohol were employed as 

 standards, the effect produced being practically the same. 



Table I* 



No. 



Solution. 



Percentage length of column 

 of residue after — 



2hrs. 



20 hrs. 



70 his. | 



22a 

 b 



d 



f 

 9 





63 -7 

 70 -0 

 60-5 

 59 -9 

 66 -2 

 63 -3 



63 o 



62 -2 



63 -3 

 55 -2 

 61 -5 

 57 -1 

 63-3 



63-5 

 63-4 

 63 -4 

 54 -0 



61- 

 54-9 



62- 5 | 



Water 



Sodium chloride, "3 molar 



„ 0-1 „ 



o-i „ 



It was found that when yeast was treated with water the cells at first 

 increased in volume, but later returned to their original state. An initial 

 dilatation also occurred with decimolar solutions of sodium chloride and 

 sodium phosphate, but eventually, in both these cases, a slight amount of 

 plasmolysis was noted. With 03 molar concentrations of these substances 

 no increase in volume was observed, and a considerably greater final degree 

 of plasmolysis was produced than was the case with the weaker solutions. 



These numbers show, further, that equilibrium is practically established 

 in 20 hours at air temperature, but not in 2 hours. 



Adrian Brown (loc. cit.) finds that solutions of certain non-electrolytes 

 seem to possess the power of entering the barley grain, whilst others, such 

 as sugar and urea., do not ; also that trichloracetic acid, an acid which 

 becomes strongly ionised in dilute solution, enters quite freely. The fact 

 that most of the entering substances are non-electrolytes, he observes, 



