146 PHYSIOLOGY OF NUTRITION. 



of Tradescantia, with plasmolysing solutions to which pigments 

 have been added, 



I conducted investigations of this kind in the following manner : 

 Strips of epidermis from leaves of Tradescantia were plasmolysed 

 as above described by means of a solution of common salt, and 

 then laid in juice obtained by crushing fairly dark-coloured 

 cherries. The colouring matter can traverse the cell-wall ; it 

 penetrates into the space intervening between this and the proto- 

 plasm, but the protoplasm itself does not take it up. If epidermal 

 cells of Tradescantia are first plasmolysed, then killed, by dipping 

 the strips of epidermis in hot water, and finally laid in cherry 

 juice, the protoplasm and the nucleus stain fairly deeply, the dead 

 protoplasm being readily permeable to many substances which in 

 the living condition it is unable to take up. 



To prove that normally protoplasm is impermeable, but after 

 death is permeable to sugar, we carefully rinse a few pieces of 

 beetroot, and then transfer them to distilled water at the ordinary 

 room temperature, some of them at once, the rest after they have 

 been killed with hot water. After a few hours we take from the 

 fluids small test quantities, add to them a few drops of dilute 

 Hydrochloric acid, and boil for a short time; the presence of 

 sugar can easily be detected by means of Fehling's solution in the 

 fluid which has been in contact with the killed pieces of beetroot, 

 whereas the others contain no sugar. 



To prove that the normal hyaloplasm is also frequently imper- 

 meable to mineral substances, we prepare 24 per cent, solutions 

 of Sodium chloride or Potassium nitrate. In these we place hairs 

 from the stamens of Tradescantia, or strips of epidermis from the 

 underside of the midrib of the leaf of Tradescantia discolor. The 

 cells of T. discolor, a plant which can be obtained at any time of 

 the year, and which must be grown under cover, have a coloured 

 cell-sap. The solutions make their way through the cell- walls into 

 the cells. Plasmolysis follows in the course of one to two hours, 

 and it still persists if the objects are left in the salt solution 

 for several hours longer. It is this which is of special importance 

 to us, since if the protoplasm were, under the conditions described, 

 permeable to Sodium chloride or Potassium nitrate, it would 

 gradually, with increasing osmotic capacity of the cell-sap, swell 

 out again in each cell. 1 



The diosmotic properties of the living hyaloplasm on the one 

 hand and of the cell-wall on the other are, as we know, very 



