EXCITATION AND TRANSMISSION 85 
days, or weeks, the gradient usually becomes to some 
extent more or less permanently recorded in the proto- 
plasmic substratum. Concerning the exact nature of 
this record we can only say that it consists primarily in 
the factors determining the rate of fundamental proto- 
plasmic activity, for we see that the differences in rate 
persist. The persistence of the gradient as a gradient 
must depend upon the fact that the changes in the 
protoplasmic substratum go on more rapidly at the 
higher levels than elsewhere. In short, I believe that 
the determination by an external factor of a more or less 
persistent gradient in physiological condition is the most 
general case of incomplete reversibility of excitation and 
also of so-called functional adaptation, that is, the 
process of the more or less persistent alteration of 
protoplasmic structure and function by the dynamic 
activity occurring in it. 
GENERAL DISCUSSION 
Concerning the existence of the axial gradients and 
their significance in development there can be no doubt. 
These are demonstrated facts, however we may inter- 
pret them, and they are the earliest indications of an 
order or pattern on a larger scale than that of proto- 
plasm. Organismic pattern is, as already noted, a 
pattern of regions or masses of protoplasm or cells and 
of a higher order of magnitude than protoplasmic 
pattern; physiological polarity and symmetry appear 
in protoplasms of very different specific constitution 
and many different lines of evidence agree in indicat- 
ing that they are primarily quantitative gradations 
in physiological condition, and that they can be 
