4o A CHEMICAL SIGN OF LIFE 
In the next place, it was thought possible that our 
assumption that the condition under which an electrical 
decomposition takes place is the same in a living and 
dead nerve may not be strictly true, but that an electrical 
current can in some way drive away carbon dioxide more 
quickly in the living nerve. Since killing by steam may 
also drive out the gas already present in the tissue, the 
apparent indifference of the dead nerve toward electrical 
stimulation may not prove that the increased carbon 
dioxide accompanying stimulation in the living nerve is 
really a direct result of a change in its vitality, rather 
than an indirect result of the passage of the electrical cur- 
rent. If, however, this increased gas production were 
due to the mere electrical decomposition, which was not 
limited to the point of contact with the electrode, we 
ought in the living nerve to get a proportional increase of 
carbon dioxide by increasing the length of nerve through 
which the current directly passes. The fact is, however, 
that we can produce an increase of carbon dioxide by 
stimulating with electrodes 2 mm. apart, so that only a 
small portion of the nerve is traversed by the current, 
as well as by electrodes 15 mm. apart. It makes no 
difference how much of the nerve is traversed by the 
current. But it does make a difference how much of 
the nerve is traversed by the nerve impulse. These 
experiments suggest very strongly that the increase of 
carbon dioxide on: electrical stimulation is due to the 
increased metabolic activity during functional activity 
in the nerve, and is not due to the influence of the 
electrical current as such. With the aid of other 
means of stimulation we shall now proceed to prove 
that all stimulation is accompanied by an increase of 
