CHEMICAL SIGNS OF LIFE gi 
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 asdoseeds. 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 
