PHYSICS OF SEGMENTATION. 1 05 



case is possible only if it is either the immediate result or cause of a 

 change in the potential of that energy which is opposed to the 

 surface tension, viz., osmotic, /. e., the " repelling " forces of the 

 substance in solution. 1 The change in surface tension is one 

 part of the " Ausgleichung " of the potential difference existing 

 between it and the potential opposing it, viz., osmotic pressure. 

 The necessary coexistence of these two kinds of energy in a 

 solution and the characteristics of each bring it about however 

 that when one potential decreases the other does also, although 

 there may be a relative fall of one and rise of the other, thus 

 making an isocyclic event possible. For just as the surface 

 tension decreases with an increase in surface and conversely, so 

 also is a decrease in osmotic pressure accompanied normally by 

 an increase in volume (and therefore of surface) and conversely. 

 It is evident then that in segmentation with its change of form 

 and redistribution of surface tension we are always dealing im- 

 mediately with the interrelations of two energy forms, surface and 

 osmotic, and mediately with any causes which may act on them, 

 whatever these may be. If we succeed in showing that the 

 various physical agents used for producing artificial partheno- 

 genesis can be effective only by in any case causing changes in 

 either one or both of these energies, then we shall have obtained 

 that unification of evidence which is our purpose. 



4. FACTORS CONDITIONING VARIATIONS AND CHANGES IN 



THESE ENERGIES. 



The existence of an uncompensated potential difference within 

 the egg can be accounted for in two ways. It may be either 

 the result of changes already going on in the egg, e. g., the 

 becoming active of preferments 2 and so the formation of new 

 chemical compounds, processes of maturation, or those leading 

 to " natural death," 3 but this is the same as saying that such a 

 difference is already there and that it leads to others ; or the 



1 In reply to the possible objection that colloidal solutions have no osmotic pres- 

 sure there is experimental evidence that they have this and are diffusible, thus showing 

 that there is no essential difference between these and other solutions. Cf. Hober, 

 " Physikalische Chemie der Zelle u. Gewebe," s. 43, et seq. 



2 Cf. Hofmeister, " Chemische Organization der Zelle." 



3 J. Loeb, BIOL. BULL., Nov., 1902, " Maturation, Death, etc., in Asterias." 



