14 E. J. LUND 



we find in support of such an interpretation of the process of 

 dedifferentiation and differentiation? 



VII. ROLE OF REVERSIBILITY IN CELL PROCESSES 



Reversibility of many processes in living matter is one of the 

 fundamental dynamic characteristics of organisms. A physical- 

 chemical system which is reversible is a self regulatory system at 

 least in so far as its equilibrium conditions are concerned. Living 

 organisms make use of a large number of such self equilibrating 

 systems, for example the mechanism for maintaining the acid- 

 base equilibrium in the body; many chemical mechanisms con- 

 cerned with translocation of fats, carbohydrates and proteins in 

 plants and animals under different conditions; the reversible 

 character of the permeability of plasma membranes. The re- 

 sults of Loeb ('14) indicate that the processes antecedent to 

 cleavage in artificial parthenogenesis have a reversible character. 

 Many other instances of reversibility might be mentioned. 

 Evidence of visibly reversible gelation and liquefaction trans- 

 formations in living protoplasmic structures of cells has been 

 given by Kite ('13) and recently by Chambers ('15) and ('17). 

 They seem to be very similar in nature to the processes described 

 for Bursaria, and suggest very strongly that differential gelation 

 and liquefaction processes play a large role in cell morphogenesis. 



To what known biological or chemical processes can we look for 

 an explanation of such gelation and liquefaction processes in 

 living cells? I believe that many intracellular chemical pro- 

 cesses of which we have at present some definite knowledge will 

 help to throw light on the mechanism of dedifferentiation. I 

 have in mind particularly the familiar phenomenon of auto- 

 lysis. Many different endoenyzmes, in themselves perhaps the 

 expression of surface effects (Bayliss, '14) occur in protoplasm, 

 whose actions are inhibited and controlled under normal condi- 

 tions of metabolic* equilibrium. Autolysis leading to a disin- 

 tegration of complex proteins (dedifferentiation?) of the cell 

 takes place in practically all cells when the normal income of 

 the cells is withheld. For example in the yeast cell, so long as 

 food is available there is little evidence of self digestion. But 



