EXCITATION AND TRANSMISSION 77 
regions of less rapid oxidation like a region of excitation 
with respect to less excited or unexcited regions, i.e., it 
becomes electronegative and a current similar to the 
excitation current is set up between it and other less 
rapidly oxidizing regions. If this current constitutes 
the exciting factor for adjoining regions and so the 
primary factor in transmission, then a region of rapid 
oxidation, however determined, may initiate a process 
of transmission which induces excitation, involving 
increase in the rate of oxidation at points within the 
range of effectiveness of the current, and so may give 
rise to an oxidation gradient. Doubtless even in such 
a case membrane changes are involved, but my point is 
merely that they need not necessarily be regarded as 
the most significant changes in the complex process. 
In some of his later papers Lillie calls attention to the 
probable significance of oxidation-reduction in the more 
primitive excitation-transmission relations. 
In such a process as this the velocity of transmission 
may be very low as compared with nerve, so low indeed 
that it might in many cases scarcely be termed trans- 
mission in the ordinary sense. Moreover, in such a 
process a decrement is to be expected, since a relation 
unquestionably exists between the electrical condition 
and the rate of oxidation, and this being the case a 
gradient must result. In fact, in the extreme case such 
a gradient may arise without any wavelike transmission 
of excitation, such as occurs in the nerve, electrical 
transmission only being involved and determining a 
gradation in rate of oxidation and associated condi- 
tions from the original region of high rate to a certain 
limit of distance. 
