PERSPECTIVES IN EVOLUTION — RITCHIE 253 



But it is just as obvious that none of these interpretations reach 

 the secret spring of life itself. The physical explanation of the 

 architecture of animals must assume the power of the living thing 

 to react and mould itself to the forces that play upon it. Osmotic 

 reactions do not explain wholly the exchange between cells and their 

 surroundings, as Gross (1939) found in the diatom Ditylum hright- 

 loelli, in which his experiments led him to postulate a vital activity 

 of the cells involving perhaps the secretion of water, a supposition 

 since confirmed by Bhatia (1940) working with Gross in the depart- 

 ment of zoology of Edinburgh University. The Donnan equilibrium, 

 which interprets a condition of thermodynamical balance, meets the 

 case of a living cell only when the cell activity is at its lowest; and 

 the more active, that is the more alive, a cell is the less does the 

 Donnan theory become applicable. 



No known law can account for the curious way in which substances 

 are sorted out and grouped on opposite sides of living membrane. 

 It has been shown to be widely true that on one side of living proto- 

 plasm acid is produced (as in the stomach) together with a higher 

 concentration of potassium, ammonium, phosphate and, if they be 

 introduced into the blood, basic dyes; whereas on the other side 

 occurs sodium (on the blood side of the stomach) associated with 

 the production of alkaline substances and the assembling of intro- 

 duced acid dyes. Such anomalous grouping is repeated in plant 

 cells which produce acid and potassium concentrate on the inner side 

 and, on the other side of a protoplasmic film only one-hundredth of 

 a millimeter thick, alkali and calcium concentrate. As Keller (1938) , 

 in his survey of these odd contrasting groups, sums up the situation : 

 "We cannot explain how a unipolar living electrode is able to pro- 

 duce or concentrate on one side acid and the potassium group, on 

 the other alkali and the sodium group, but we have to accept this 

 fact as generally observed in all animal and plant cells as long as 

 the electric potentials of the cells are normal and the normal oxygen 

 supply is at the disposal of the cells." 



Enzymes may be necessary for the complete activity of a cell, but 

 though it may hasten a chemical reaction no catalyst can set a 

 reaction in motion; in the case of the cell that appears to be the 

 prerogative of "life." 



Minute analysis still stops short of the secret of life. 



THE QUALITY OF LIFE IN PERSPECTIVE 



Let us turn, then, from the minute analysis of the imit of life, 

 which in recent years has done so much to reduce the mystery of 

 life, without however reaching the kernel of the mystery, to see 

 what suggestion may arise from another point of view, a perspective 

 of evolutionary processes. 



