GROWTH, METAMORPHOSIS AND DEVELOPMENT 253 



"After all, I believe I may make the assertion that the creation 

 of these pictures is due to a new and hitherto unrecognized 

 force. It has nothing in common with magnetism, electricity 

 or galvanism. It is not stimulated or created by any external 

 force but is innate in substances and becomes active when their 

 chemical affinities neutralize themselves; that is, they undergo 

 selective attractions or repulsions, and thus combine or sepa- 

 rate. I call this force ' Formative Instinct ' and regard it as 

 the prototype of the 'vital force' of plants and animals." 



Of course, no special "Force" need be invoked for the explanation 

 of RUNGE'S pictures. They are the result of very complicated 

 diffusion and capillary phenomena associated with chemical trans- 

 formations. 



What is especially interesting in RUNGE'S pictures, on the one 

 hand, is the constancy of the forms obtained by employing similar 

 substances, and on the other hand, the extraordinary multiplicity 

 brought about by the diverse action of different substances. 



If we let a drop of copper sulphate solution fall on a piece of 

 filter paper moistened with potassium hydrate, at the surfaces of 

 contact a membrane of copper hydroxid forms, which changes 

 rapidly but always in the same way. If we always employ the potas- 

 sium hydrate and copper sulphate in the same concentration, the 

 copper hydroxid boundary will always have the identical form, 

 provided the same filter paper is used. A change in the concen- 

 tration of one or the other ingredients, however, gives a membrane 

 of different shape. If, instead of copper sulphate, we place a drop 

 of copper nitrate on the paper, we obtain forms entirely different, 

 and a drop of nickel sulphate changes the picture completely. We 

 thus see that small variations in the concentration of the solutions 

 and in their chemical composition possess numerous possibilities 

 for the formation of new shapes. 



In the living organism variations in concentration perpetually occur. 

 We know from biological reactions that not only different animals, 

 as, for instance, sheep and lions, have chemically different tissues, but 

 that even fthe ass and the horse, and indeed different races of men, 

 may be chemically differentiated; consequently the second condition 

 for variation in form is also given, namely, the difference in chemical 

 composition. The processes of the body (organism) are regulated by 

 its colloidal state, and this very colloidal state also permits the reten- 

 tion of shapes. 



If we seek to leave this far too general point of view and study 

 details of the question more closely, we encounter almost insur- 

 mountable difficulties. 



If a small lump of copper sulphate is thrown into a dilute solution 



