128 life's beginning on the earth 



gelatinous. This brown material forms an envelope around 

 the entire prussiate, both the dissolved and the undissolved. 

 This envelope is a semi-permeable membrane of the same 

 type as the one surrounding the gelatin-tannic acid cell of 

 Traube, page 112. It allows only water to pass, none of the 

 dissolved salts. In the solution surrounding the crystal, 

 the yellow prussiate is dissolved up to 28 per cent, this being 

 the concentration of a saturated solution of that salt. Dur- 

 ing the first minute or so, the envelope is a nearly rounded 

 bag, containing a solution of the prussiate and in addition 

 some as yet undissolved prussiate. More and more of the 

 latter is dissolved by water rushing inside the membrane, 

 forming and maintaining a 28% solution, while the original 

 1% copper solution is still outside. The osmotic pressure 

 inside thus greatly exceeds the small opposing osmotic 

 pressure of the copper salt outside. More water rushes 

 into the cell and continues to expand it at a visible rate. 

 More salt goes into solution as more water is drawn into the 

 envelope. The result is that the envelope no longer main- 

 tains the simple round shape. It assumes a complicated 

 form resembling the growth of a plant. Observe the second 

 and third diagrams of Figure 38. 



A similar structure can be produced under reversed con- 

 ditions by preparing a dilute solution of yellow prussiate 

 into which a crystal of copper sulfate is dropped. Hut 

 since this copper salt is only sparingly soluble, it is better 

 to use mixtures of solid cane sugar and copper sulfate, 

 moulding this mixture into a pill which is dropped into the 

 prussiate solution. The sugar is helpful on account of its 

 greater solubility, which promotes expansion and subse- 

 quent growth. Figure 39 is a photograph of a structure 

 which develops by following this procedure. Its appear- 

 ance resembles a plant with leaves and ramified branches. 



Artificial structures develop from numerous other inter- 



