16 THE NATURE OF LIFE 



with, the absorption of water. This ap- 

 pears to be the essential thing. 



If growth consists of the absorption 

 of water can this serve as a test to dis- 

 tinguish the Kving from the dead.f^ As 

 we have seen, absorption of water takes 

 place by imbibition or by osmosis. Im- 

 bibition cannot serve as a mark of dis- 

 tinction for it goes on in the same way 

 in dead and in living seeds. If we are 

 to employ growth as a test of life it can 

 be only on the ground that osmosis is 

 in some way peculiarly characteristic of 

 living cells. Let us see whether this is 

 the case. 



One way of attacking this question is 

 to attempt to make an artificial cell 

 which will act like the living. We may 

 employ for this purpose two solutions, 

 A and B, such that a drop of A intro- 

 duced into a vessel containing B will 

 react with it and form a membrane 

 which is impervious to both A and jB, 

 but is permeable to water. We have now 

 what we may for convenience call an ar- 



