No. 402.] THE NEURONE THEORY. 463 
the nerve fibres. If the neurone is only a cell, it should then 
show the general properties of a cell, and it is from this stand- 
point that the neurone theory has been most satisfactorily 
tested. In this connection it is necessary to examine briefly 
the development of nerves, the degeneration and regeneration 
of nerves, and the nature of the neuropile. 
The development of a nerve was early sketched by Remak 
(1836) and by Schwann (1839) ; both maintained that each fibre 
consisted of a series of cells fused end to end. This view was 
accepted by many later investigators, 
notably by the English embryologist 
Balfour, who showed that in the elas- 
mobranch fishes the nerve fibres were 
early represented by lines of cells. 
This hypothesis of the chain structure 
of nerve fibres was not, however, with- 
out its opponents. Von Kupffer seems 
to have been the first to catch the idea 
that at least the core or axis cylinder of pipi ET sa tieng pica 
a nerve fibre was an outgrowth from — CPig Ta com ot aD Four 
the ganglion cell. This view was sub- cells are shown in pro 
sequently supported by others, especially ^ future nerve pora E nies 
by His, whose brilliant investigations cells have extended beyond the 
í limits of the cord; those of th 
on the development of the nerves show two other cells still lie within 
beyond a doubt that the axis cylinder . 
is an outgrowth from a ganglion cell (Fig. 2). The forming 
axis cylinders may become surrounded by cells that eventually 
develop into the sheath cells of the fibre, and these undoubtedly 
formed the lines of cells mistaken by many investigators for 
developing nerve fibres. The resolution of a nerve fibre into a 
chain of cells, as implied in Remak’s original description, is 
entirely at variance with the neurone theory, but the establish- 
ment of the idea that the essential part of every nerve fibre, the 
axis cylinder, is an outgrowth of a ganglion cell is in perfect 
accord with it. In the development of its parts, the neurone 
acts asa single cell; its processes, the axis cylinders of the 
nerve fibres, are its outgrowths. 
The degeneration and regeneration of nerves also afford an 
