98 A CHEMICAL SIGN OF LIFE 
found to run in nerves between the two cut ends of the 
nerve, up or down it, as the case may be. Evidently 
electrical current is generated in a nerve between two 
parts which are unequally irritable, or unequally under- 
going chemical change. The part of the nerve which 
is respiring most is in a different electrical state from that 
which is respiring less, and thus we see the very clear 
and definite relationship between the chemical and the 
electrical changes which have been particularly dwelt 
upon by Waller. This is one of the most important and 
fundamental discoveries which we have noted, for it 
means that there must be a decrement in the rate of the 
impulse as it flows down the fiber, and that the distance 
to which a nerve impulse can be transmitted is not 
indefinite, but that that impulse diminishes as it pro- 
ceeds, and will ultimately die out. In the medullated 
nerves, to be sure, this decrement is not large, for it is 
very necessary that it should be as small as possible in 
the more highly developed nerves; but it is to be found 
everywhere. And in simple undifferentiated proto- 
plasm of plants and animals it is easily shown to exist. 
The more rapidly nerves respire the faster do they 
appear to carry the impulse; irritability and the rate 
of production of carbon dioxide in resting nerves thus 
appear to be correlated. The more respiration the 
more life! If we abolish respiration temporarily, or 
reduce it, we find that irritability has been reduced in 
somewhat the same proportion. Anesthetized nerves 
of all kinds show a reduced output of carbon dioxide, 
and they recover their irritability when they breathe 
again. Anesthetics do not, therefore, affect the physical 
state of the protoplasm only, as they have been supposed 
