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 



