254 COLLOIDS IN BIOLOGY AND- MEDICINE 



of potassium ferrocyanid, there will soon develop a brown envelope 

 which throws out upward-growing runners, and in half an hour's 

 time the fluid is filled with figures which vividly recall both the 

 shape and the color of seaweed; if a small amount (0.5 per cent) of 

 gelatin has been added to the water, the figures have some stability. 

 Their development is easily explained: the copper sulphate dis- 

 solves and immediately forms a semipermeable membrane of copper 

 ferrocyanid, through which no copper sulphate can escape, but water 

 may enter. Since a concentrated solution of copper sulphate is 

 formed within, water will be absorbed until the membrane bursts, 

 whereupon the copper sulphate solution is brought into contact 

 with the potassium ferrocyanid again and forms a new pellicle of 

 copper ferrocyanid, and thus the process goes on. 



STEPHANE LEDUC has studied these figures most industriously 

 and has discussed their significance in numerous publications. 1 



Some of his directions are here given: Prepare granules of 1 part 

 sugar and 1 or 2 parts copper sulphate. This is scattered in a fluid 

 consisting of 100 parts of water and from 10 to 20 parts 10 per cent 

 gelatin, 5 to 10 parts saturated potassium ferrocyanid solution and 

 5 to 10 parts saturated sodium chlorid solution, which mixture has 

 been heated to 40 degrees Centigrade. In this way we obtain figures 

 like that in Fig. 41, which may attain a height of 40 cm. The gelatin 

 is solidified by cooling and the figures may be preserved. Other fig- 

 ures are obtained by throwing granules of fused calcium chlorid or 

 barium chlorid into a concentrated solution of soda. 



Another recipe is: 



Water 1 liter 



33 per cent potassium water glass solution 60 gm. 



Saturated soda solution 60 gm. 



Saturated sodium phosphate solution 60 gm. 



Beautiful branching figures are given by scattering calcium chlorid 

 granules in this mixture. 



The more concentrated the solutions, the more rapid is the growth 

 and the more branching and delicate are the shapes. If the outer 

 water is diluted while the growth is in progress, we may produce 

 figures with stems and tops, like fungi (mushrooms and toadstools, 

 etc.). These figures react to small changes in osmotic pressures by 

 changing their shape. 



VI shall mention only his latest publications: St. Leduc, Biochem. Ztschr. 

 (Festband f. H. J. Hamburger), 1908, 280 u. ff. Les croissances osmotiques et 

 l'origine des etres vivants (Bar-le-Duc, 1909). Les bases physiques de la vie et 

 la biogenSse (Presse Medicale, 7, 12, 1909). Theorie physico-chimique de la vie 

 (Paris, 1910), La dynamique de la vie (A. Poinat, Paris, 1913); and many others. 



