18 THE NATURE OF LIFE 



In both the living and the artilBcial 

 cell growth is quickened by increase of 

 temperature. In the living cell there is 

 an upper limit of temperature beyond 

 which no growth takes place. This 

 seems to be due to the proteins of the 

 living cell. If we could employ such pro- 

 teins in the membrane of the artificial 

 cell we might obtain a similar result. 



The rate of growth depends, in the 

 living as in the artificial cell on the sup- 

 ply of substances within the membrane 

 which can attract water. In the case of 

 the living cell these are mostly sugars, 

 organic acids, salts, and so on, and we 

 can employ these same substances in the 

 artificial cell. In the living cell we often 

 find starch, which takes little part in 

 attracting water but which may be grad- 

 ually transformed into sugar which at- 

 tracts water actively. In the same way 

 we may place starch in the artificial cell 

 and have it slowly transformed to sugar 

 and thereby cause the cell to take up 

 water. 



