CH. v] traube's cell. 123 



(142) Trauhes artificial cell\ 



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 byPfefferl 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. 



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'^. 



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



1 Traube in Arcliiv filr Anatomic und Physiologie (Reichert and Du 

 Bois-Reymond), 1867. - OsmotiscJie Untermchungen, 1877. 



3 In the first edition of this book I recommended copper sulphide for 

 Traube's experiment, — a piece of advice which somewhat puzzled my 

 friends and reviewers. We have been in the habit of using for experiment 

 142 a sample of commercial copper sulphide because the cells which it 

 forms "grow" better than those produced by CuSOj. And I re- 

 commended its use without ascertaining that (as turns out to be the 

 case) the result is entirely due to the presence of a soluble copper salt in 

 our sulphide. [F. D. 1895.] 



•* See de Vries, Bot. Zeitunp, 1885, p. 1. 



