78 THE NATURE OF LIFE 



the delicate membranes in the proto- 

 plasm. If this is the case it is easy to 

 see that new reactions may be started 

 which may produce the bending of the 

 root. 



In view of what is said above it is not 

 surprising that on cutting or crushing a 

 tissue an increased evolution of carbon 

 dioxide is observed. Since this does not 

 occur in tissues killed by heating it has 

 been called by Tashiro a sign of life. Mr. 

 Davies, working in the writer's labora- 

 tory, found that cells killed by acetone 

 continue to give off carbon dioxide after 

 death and that when such dead cells are 

 crushed there is a very marked and im- 

 mediate increase in the amount of carbon 

 dioxide given off. Hence it would seem 

 that this is not properly to be considered 

 a sign of life. 



A similar behavior is to be expected in 

 any non-living system in which mechani- 

 cal agitation brings into better contact 

 substances which produce carbon dioxide. 

 To what extent this would imitate what 



