SYNTHETIC BIOLOGY 119 



ease the capillarity of the paper necessarily exerts a certain 

 influence on the formation of the figures, but in addition to 

 this, Runge admits the intervention of another force hitherto 

 unknown, which he calls ' Bildungstrieb, 1 the formative 

 impulse, which he considers to be the elementary vital force 

 in the formation of plants and animals. 



'"In 1867, R. Bottger obtained arborescent forms and 

 ramifications of metallic vegetation by sowing fragments the 

 size of a pea of crystals of the iron chlorides, chloride of 

 cobalt, sulphate of manganese, nitrate and chloride of copper, 

 etc., in an aqueous solution of silicate of sodium of specific 

 gravity 1 "18. These forms are due, as I shall show later 

 on, to the surface tension of the oily precipitate ; Bottger gives 

 no explanation of the phenomenon. 



"To this force, viz. that of surface tension, is also due the 

 cellular forms obtained by Traube in LSb'b'. These were 

 obtained from gelatine and tannin, from acetate of copper or 

 lead, and from nitrate of mercury in an aqueous solution of 

 ferrocyanide of potassium. These cells and precipitated 

 membranes have also been studied by Reinke, F. Cohn, H. de 

 Vries, and myself, who all observed the regression of these 

 membranes, which although colloidal at the beginning of the 

 reaction speedily become friable. This entirely refutes the 

 opinion of Traube as to the constitution of the precipitated 

 membranes. He supposed them to consist of masses of solid 

 substance, with smaller orifices which do not permit the 

 passage of the membranogenous substance, whilst the larger 

 orifices through which it can pass are soon closed by the 

 precipitate, the membrane itself thus growing by a process 

 of intussusception. 



" Later on Traube himself considered the precipitated 

 membrane to be a thin, solid gelatinous layer in which the water 

 was mechanically entangled. 



"Tamilian has also made a number of experiments with 

 solutions of the chlorides and sulphates of the heavy metals, 

 and solutions of phosphates, silicates, ferrocyanides, and other 

 salts. He found that most of these membranes were permeable 

 to the membranogenous solution. According to Tamilian, all 



