CHEMICAL SIGNS OF LIFE 91 



Is an injury a stimulation? Are we justified in 

 regarding the increase of carbon dioxide following injury 

 by crushing as in the same category as the increase of 

 carbon dioxide production by ordinary stimulation? 

 That this conclusion is justified is shown by the fact 

 that such an acceleration of carbon dioxide production 

 will not take place in inexcitable tissue. Neither killed 

 nor narcotized tissue can be made to give off more carbon 

 dioxide when crushed. Response to an injury is given 

 by living irritable tissue only. It is impossible to injure 

 the dead tissue. 



Other tissues. When we discovered that the irrita- 

 bility of a kernel of wheat and that of the nerve fiber are 

 identical, so far as their metabolic expressions are con- 

 cerned i.e., no irritability without resting metabolism, 

 increased metabolism on stimulation, and changes in 

 metabolic condition, according to the state of excita- 

 bility we thought it might be possible that this similar- 

 ity between the nerve and wheat is special, and that 

 other plant tissues may not behave at all in the same 

 way as do seeds. Similar experiments were consequently 

 tried on several other seeds, including wild oats, Lincoln 

 oats, Swedish select oats, rice, corn, mustard, and various 

 others, with the result that, although the amounts of 

 carbon dioxide given off varied considerably, all living 

 seeds were found to be metabolically active. All of 

 them responded to an injury, giving off more carbon 

 dioxide on crushing. And in no case did we succeed in 

 producing more carbon dioxide on crushing killed seeds, 

 or seeds which had lost germinating power. Thus we 

 made certain that under the experimental conditions in 

 the biometer it is possible to detect the fundamental 



