542 HENRY H. DONALDSON AND G. NAGASAKA 
tinue to increase rather rapidly in diameter with the increase in 
body size. 
There appear therefore to be the following relations between 
the cells and fibers which have been chosen for study. All of 
the (largest) fibers, dorsal root fibers, the fibers just distal to the 
ganglion, and ventral root fibers increase at about the same rate 
and to about the same diameter (table 2, chart 1). The spinal 
ganglion cells increase in diameter at nearly the same rate (not 
quite so rapidly) as the fibers which come from them (table 7, 
chart 2). On the other hand, the spinal cord cells early reach 
nearly full size (tables 4, 5, and 6, chart 3), after which they grow 
very slowly. Therefore the ventral root fibers increase in diam- 
eter much more than do the cells from which they come. The 
difference in growth appears therefore to be between the two 
classes of cell bodies. 
DISCUSSION 
In the first place we note that the spinal ganglion cells are affer- 
ent neurons of the first order—and the spinal cord cells (here 
studied) are efferent neurons of the first order. In loaking for 
other differences which might explain this lack of agreement, we 
recall that the distal process (nerve fiber) from the ganglion cell 
is physiologically a dendrite—that is, it carries impulses into the 
cell body—whereas the dorsal root fibers and the ventral root 
fibers both convey impulses from the cell body. 
Growth of the axon process in diameter is not necessarily 
accompanied by a corresponding growth of the cell body, as is 
shown by the spinal cord cells. We should not, therefore, look 
for an explanation of the growth of the cell body of the spinal 
ganglion neuron as due to the enlargement of its central or axon 
process which forms a fiber in the dorsal root. If this argument is 
sound, then it is to the distal process which forms a fiber in the 
nerve trunk, but which has the function of a dendrite, that we 
must turn for an explanation. As the body surface (and the 
surface of other organs innervated by afferent fibers) increases, 
not only is the area innervated by the fiber increased, but sensory 
discrimination (the ‘local sign’) is in a measure maintained. 
