GROWTH 19 



If the artificial cell is placed in a solu- 

 tion which is more concentrated than 

 that inside the cell, water is attracted 

 from the cell to the outside solution and 

 in consequence the cell shrinks. This 

 is also true of the living cell. If it is 

 growing in tap water it can be made to 

 shrink by putting it into a sugar solution 

 which withdraws water. If replaced in 

 water it again expands. Since we regard 

 this as growth, the shrinkage may be 

 looked upon as the reversal of growth. 

 We find that many living cells may be 

 made to grow and shrink several times 

 in succession, just as in the case of the 

 artificial cell. 



If the outside solution is concentrated 

 enough to draw water out of the cell 

 it may nevertheless prevent water from 

 going in and so check growth in propor- 

 tion to its concentration. Consequently 

 by varying the concentration we may 

 accurately control the rate of growth. 



We might go on to discuss other points 

 of resemblance between the growth of 



