FURTHER EXPERIMENTS ON THE DEVELOPMENT 
OF PERIPHERAL NERVES.’ 
BY 
ROSS GRANVILLE HARRISON. 
From the Anatomical Laboratory of the Johns Hopkins University. 
WITH FIVE FIGURES. 
Two main questions have arisen in connection with the study of the 
development of the peripheral nerves. The one concerns the constitution 
of the nerve fiber, 7. e., whether it is a process of a single cell or derived 
from a chain of cells. The other has to do with the manner in which the 
connection between center and periphery is established, whether there 
is a continuity ab initio (protoplasmic bridges) or whether the connection 
is secondarily brought about by outgrowth from the center towards the 
periphery. 
Prior to the year 1904 all attempts to solve these problems were 
based on observations made upon successive stages of normal embryos. 
When one compares the careful analyses of their observations, as given 
by various authors, one cannot but be convinced of the futility of trying 
by this method to satisfy everyone that any particular view is correct. 
The only hope of settling these problems definitely lies, therefore, in ex- 
perimentation. 
The question of the constitution of the nerve fiber, whether a cell 
process or a cell chain, may here be considered first. 
If one examines a developing nerve, one sees that there are numerous 
spindle shaped cells (cells of Schwann, sheath cells) throughout its 
course, and that these are very closely attached to the young nerve fiber ; 
on the other hand, it is also found that the nerve is connected with gang- 
lion cells. The disputed point with which we here have to deal concerns 
primarily the respective rdles played by these two kinds of cells in the 
genesis of the fiber. Some time ago I described a series of experiments * 
1Read before the Association of American Anatomists at the meeting held 
at Ann Arbor, Mich., December 29, 1905. 
?Harrison, Neue Versuche und Beobachtungen tiber die Entwicklung der 
peripheren Nerven aer Wirbeltiere. Sitzungsber. d. niederrheinischen Ges. 
f. Natur u. Heilkunde. Bonn, 1904. 
AMERICAN JOURNAL OF ANATOMY.—VOL. V. 
