CHAPTER IV 
EXCITATION AND CONDUCTION 
We have shown by this study of nerves that living 
matter must necessarily undergo metabolic activity and 
that without an increase of this activity protoplasm 
will not function. In short, to be excitable, the 
protoplasm must respire, and to be excited, its meta- 
bolic activity must be accelerated. It has also been 
demonstrated that the excited state travels along the 
fiber with simultaneous increase of the metabolism. 
Although our theme in this little volume is not a 
consideration of how this state of excitation is trans- 
mitted, but is rather an analysis of the conditions 
which characterize the irritable tissue, the relation 
between these two phenomena is so close that we 
shall consider certain facts which are directly con- 
cerned with them. 
The two phases of protoplasmic irritability are 
excitability and conductivity, or transmission, of this 
excitation. Since it is very difficult experimentally to 
produce excitation without conduction, we are accus- 
tomed to consider the fundamental processes underlying 
these two processes as probably identical. There are 
certain facts which are sometimes cited as evidence that 
these phenomena are not necessarily interdependent. 
In the case of localized and partial narcosis, for instance, 
local excitability in the narcotized portion does not 
disappear simultaneously with conductivity through 
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