CHEMICAL SIGNS OF LIFE 89 



He found that this electrical change the blaze 

 current, as he called it which appeared when the living 

 seed was stimulated by a strong induction current was 

 not confined to seeds, but occurred also in other varieties 

 of living matter, such as the eyeball, skin, leaves, petals, 

 and many other tissues of plants and of animals. This 

 momentary electrical change produced thus only by 

 living matter is accordingly a reliable sign of life, since 

 it does not occur in dead matter. 



When we discovered that even a resting nerve gave 

 off carbon dioxide if we used a sensitive method, we 

 at once proceeded with some curiosity to determine 

 whether or not ordinary seed is chemically inactive. 

 We had in mind thus to test Waller's conclusion that the 

 electrical sign in the seed is really the sign of chemical 

 changes which, however, were not large enough to be 

 detected by ordinary chemical methods. 



Resting metabolism in seeds. If a few kernels of 

 wheat are placed in one chamber of the biometer, there 

 is no difficulty in showing that seeds give off carbon 

 dioxide, since a drop of barium hydroxide in the chamber 

 containing the seeds becomes covered after a time with 

 a precipitate of barium carbonate. It is true that the 

 amount of carbon dioxide given off is exceedingly small, 

 being many times less than that of the resting nerve, 

 but that this carbon dioxide is produced by a vital 

 metabolism is shown by the fact that living seeds 

 give far larger amounts of the gas than dead ones. 

 A seed respires, therefore, as long as it is alive; and 

 we can measure the amount of respiration. Of course 

 the mere production of this gas from a seed does not 

 mean necessarily that the seed is alive, for the reason 



