THE CATALYST ENTELECHY IN DIFFERENTIATION 191 



important cytoplasmic nucleotides and shows the Feulgen reac- 

 tion. 



Woerdeman 18 observed a sharp disappearance of glycogen from 

 the dorsal lip during invagination. Now it had been shown by 

 Willstatter and Rhodewald 19 that two forms of glycogen exist in 

 the cell, one readily soluble (lyoglycogen) the other comparatively 

 insoluble (desmoglycogen); and it was found that both of these 

 could induce neural tubes, because they contain, in adsorbed 

 state, some ether-soluble material in amounts so small that after 

 50 hours' extraction in a Soxhlet apparatus the solution, on 

 evaporation, left a scarcely visible residue. Yet this trace material 

 was a potent inductor. 



The view here being maintained is that the mechanism whereby 

 an undifferentiated (neighborwise) group of cells becomes con- 

 verted, irreversibly as a rule, into a differentiated (self-wise) group, 

 is a transmissible, i.e., cellularly heritable, change in biocatalysts. 

 This leads to a change in chemical output having physiological 

 and morphological consequences. Similar, but progressively more 

 specific and limited catalyst changes determine or are associated 

 with the formation, activity and location of secondary, tertiary 

 and subsequent organizers, until the various structural fields ex- 

 haust the existing possibilities and enter the adult stage of equi- 

 librium. That the equilibrium is a dynamic one, at least in some 

 respects, is shown, e.g., by the growth of skin, hair and nails, the 

 healing of wounds, and the development of abnormalities such 

 as tumors and acromegaly. 



How do there arise in a cell new or changed catalysts which 

 are transmissible to a daughter cell upon cell division? 



Nature will, no doubt, utilize somewhere every possible effec- 

 tive mechanism, and no limitations on nature are suggested in 

 the following discussion of what appear to be the principal mech- 

 anisms: 



(1) Gene mutation 



(2) Gene modification 



(3) New catalyst formation 



(4) Deflocculation and elution 



Before considering these possibilities further, it should be 

 pointed out that cellularly heritable change seems to be a basic 

 factor in the following: 



(A) The "Anlagen." An Anlage is a cell group which develops 

 into a certain organ, e.g., liver, heart. Though not always dis- 



