CHAPTER V 

 CHEMICAL SIGNS OF LIFE 



We have endeavored to show that the living nerve, 

 as long as it is irritable, is chemically active and that 

 when it functions this metabolism is accelerated. As the 

 irritability of the nerve varies, there are simultaneous 

 changes in chemical activity. What characterizes the 

 living state is respiration and its increase on stimulation. 



We have come now to our main inquiry, namely, 

 whether or not all living matter undergoes respiration 

 as long as it is alive, and whether stimulation always 

 increases its respiration. In addition, we have to ask 

 whether, if this is true, it can be used as a sign of life in 

 all living matter. 



Seeds. It has hitherto been maintained that since 

 dry seeds do not respire but are irritable, irritability is 

 independent of respiration. The work of Horace Brown, 

 Thistleton Dyer, and others indicates that dry seed can 

 be kept alive at very low temperatures in conditions 

 where no ordinary gaseous exchange is possible. It is 

 argued, therefore, that life is possible without any 

 metabolic activity. Dry seeds, kept for long periods 

 in a closed vessel, have not been found to give any evi- 

 dence of this fundamental chemical change occurring 

 in living matter, namely, the production of carbon 

 dioxide. Such seeds, it is well known, are not really 

 dead, for under proper conditions they germinate. 

 They appear to live without respiration, but this is but 



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