THE OUTGROWTH OF THE NERVE FIBER AS A 
MODE OF PROTOPLASMIC MOVEMENT 
^ ROSS GRANVILLE HARRISON 
Bronson Professor of Comparative Anatomy, Yale University 
THIRTY-TWO FIGURES 
THREE PLATES 
CONTENTS 
Introduction 787 
Early development of nerve fibers in the normal embryo 792 
Experiments upon embryonic tissues isolated in clotted lymph 799 
Description of methods 799 
General description of material 808 
Description of the behavior of nervous tissue 813 
Discussion of results 823 
The significance of the experiments in the interpretation of normal 
development 823 
The bearing of the experiments upon the theories of nerve development. . . 826 
The elementary factors of nerve development 830 
Analysis of the factors which produce the specific arrangement of the 
nerve paths 833 
Summary 841 
INTRODUCTION 
The idea that protoplasmic movement is concerned in the activ- 
ities of the nervous system has appeared in a variety of forms 
during the past twenty years. Not only has it been supposed 
that the processes of nerve cells may be extended and withdrawn, 
making and breaking connections with other cells during func- 
tional activity, but also that the movement of cells and their 
processes in the course of development has been the chief factor 
in bringing about the specific nervous connections found in the 
adult. 1 The latter idea is associated particularly with the name 
of Ramon y Cajal, who in his memoir on the retina ('92) first put 
^ Schiefferdecker ('06) has discussed at length and in an admirable way the 
extensive literature bearing upon this subject. 
