718 DR ALEXANDER BRUCE AND DR JAMES W. DAWSON ON 
in length and diameter, and the imbricating ends fuse together to form a continuous 
axis-cylinder. BaLtLaNnce and SrewartT were able to assure themselves that the 
neuroblasts, demonstrated by the Golgi method shooting out beaded axis-cylinders 
from opposite poles, were identical with the proliferated neurilemma cells, which, 
with Stroebe’s method, showed the earliest stage of a new axis-cylinder as a deposition 
along one side of the cell. The Stroebe method showed axis-cylinder intensely blue 
against a pink background. The new myelin sheath is also laid down by a process 
of secretion along one side of a spindle-shaped neurilemma cell, probably being wrapped 
round a pre-formed axis-cylinder. It grows in length, shows like the axis-cylinder 
a beaded appearance, and ultimately anastomoses with adjoining sheaths. The beaded 
appearance of the myelin sheath is due to the presence of the nucleus of the cell 
in which it is developed: as the sheath grows in size the nucleus becomes less 
conspicuous and finally can be found only in each internode. Within a graft the 
neuroblasts. are developed from the proliferation of neurilemma cells of the proximal 
and distal segments. They travel into the graft alongside the blood-vessels, for the 
embryonic sheaths are found in greatest abundance in the immediate vicinity of 
the vessels. The graft is therefore a scaffolding invaded by neurilemma cells, 
predisposed to assume a longitudinal direction, within which new axis-cylinders and 
myelin sheaths are secreted. 
The difference between the changes which characterise regeneration in a re- 
united nerve and in the distal segment of a non-united nerve is one merely of degree 
and not of kind. Even in the latter case regeneration of the axis-cylinders and the 
myelin sheaths takes place, although full maturity of the nerve fibre is not attained 
unless the distal segment be joined to the proximal so that their fibres may become 
functionally continuous. In both axis-cylinder and myelin sheath the beaded stage is 
apparently the limit of development in cases where functional conductivity is not 
re-established. 
BALLANCE and STEWART are convinced upholders of the view of the multicellular 
structure of the peripheral nerve fibre and of the neuroblastic function of the neuri- 
lemma cells. They believe that the peripheral nervous system is to be considered as 
made up of a chain of cells, and further, that the activity of one variety of cell, and 
one variety only—the neurilemma cell,—is responsible for the regeneration of a 
peripheral nerve, not only for its axis-cylinder but also for its myelin and neurilemma 
sheaths. 
BETHE (1901-1907) is at present the most prominent and strenuous supporter of 
the peripherist theory, and his work since the beginning of the century has formed 
the main point of attack of the centralists. After a very complete series of experi- 
ments, which has seemed to exclude every possible fallacy, he sets himself to answer 
the following questions :—Can regeneration be purely central? Or purely peripheral ? 
Or does it rest upon a co-operation of both central and peripheral influences? If this 
last, how can the share of each be determined? It is impossible to give a complete 
