246 INITIATIVE IN EVOLUTION 



" The integrating power of the nervous system has, in fact, in the 

 higher animal more than in the lower, constructed from a mere 

 collection of organs and segments a functional unity, an individual 

 of more perfected solidarity," also " a single momentary shock 

 produces in the nervous arc a facilitating influence on a subsequent 

 stimulus applied even 1400<r later." I will give but one more 

 statement from this work which seems to tell against my humble 

 position of initiative in evolution. Professor Sherrington says 

 at the end of his book, speaking of the adjustments of nervous 

 reactions in the lifetime of the individual : " These adjustments 

 though not transmitted to the offspring yet in higher animals 

 form the most potent internal condition for enabling the species 

 to maintain and increase in sum its dominance over the environ- 

 ment in which it is immersed." A little care in reading the fore- 

 going chapters will show that this in no way contradicts the views 

 expressed. 



Facilitation. 



From Professor Starling's Principles of Human Physiology 

 I may again quote part of his account of Facilitation or " Bahnung." 

 " When an impulse has passed through a certain set of neurones 

 to the exclusion of others it will tend, other things being equal, to 

 take the same course on a future occasion, and each time it traverses 

 this path the resistance in the path will be smaller. Education 

 is the laying down of nerve-channels in the central nervous system, 

 while still plastic, by the process of ' Bahnung ' along fit paths 

 combined with inhibition (by pain) in the other unfit paths . Memory 

 itself has the process of facilitation for its neural basis," again, 

 " stimulation of one anterior root produces no definite movement 

 of a group of muscles, but partial contraction of a number of muscles 

 which do not normally contract simultaneously . Thus, stimulation 

 of a sensory nerve may provoke either flexion or extension of a 

 limb, not both simultaneously. Stimulation of the motor roots 

 Will cause simultaneous contraction of both flexor and extensor 

 muscles. It is this subordination of morphological to physiological 

 arrangements in the limbs which has necessitated the foundation 

 of limb-plexuses." (Italics not in the original). Professor Graham 

 Kerr in his work on Embryology before mentioned says: " In early 

 stages of Evolution, whether phylogenetic or ontogenetic, we may 

 take it that vital impulses flitted hither and thither in an indefinite 

 manner within the living substance and that one of the features of 

 progressive evolution has been the gradual more and more precise 

 definition of the pathways of particular types of impulse, as well 



