CH. v] TRAUBE'S CELL. 123 



(142) Traubes artificial cell 1 . 



Traube's method is of great interest as a graphic way 

 of demonstrating the possibility of pressure arising 

 osmotically inside a cell. The method is moreover 

 capable of giving results of great value, especially as 

 modified by Pfeffer 2 . The following experiment is merely 

 meant to serve as a demonstration. 



Fill a beaker with a solution (2 or 3 per cent.) of 

 potassium ferrocyanide and drop it into a fragment of 

 copper chloride or acetate. The copper salt is instantly 

 coated with a precipitated membrane of copper ferro- 

 cyanide. We have found that inferior samples of com- 

 mercial copper sulphide, which contain small amounts of 

 soluble copper salts, give especially good results. 



In the artificial cell so produced osmotic pressure 

 arises by which the brittle cell-wall is broken, but is 

 instantly mended by the formation of a fresh precipitate : 

 as soon as the wall is mended the pressure inside again 

 increases, and again ruptures the cell- wall, and thus by a 

 series of breaks, healed as soon as made, an apparently 

 continuous growth of the cell takes place. 



(143) Slowness of diffusion 9 . 



Fill a tall narrow jar with water and with the help of 



1 Traube in Archiv fur Anatomie und Physiologic (Eeichert and Du 

 Bois-Reymond), 1867. 



2 Osmotische Untersuchungen, 1877. 



8 See de Vries, Bot. Zeitung, 1885, p. 1. 



