DIAMETERS OF NERVE CELLS AND FIBERS Sow 
3. The ganglion cells continue to increase in diameter with the 
growth of the rat, and in the largest group (as indicated in the 
condensed table 7) have a diameter about 1.6 times that found in 
the smallest group. The ratio between the diameters of the 
ganglion cells and those of the fibers arising from them decreases 
somewhat with increasing body size, showing that the fibers are 
increasing in diameter slightly more rapidly than is the cell body 
(table 7); but in general the. cell is enlarging nearly in proportion 
to its entire fibers, but less rapidly than the corresponding axes. 
This enlargement of the ganglion cells is accompanied by a rela- 
tive overgrowth of the cytoplasm as shown by the nucleus-plasma 
relation, and further a study of the volumes of the ganglion cells 
shows them to increase in volume in direct proportion to the 
enlargement of the area or skin surface of the rat (table 9). 
This enlargement of the cell is considered as an adaptation for 
maintaining the sensory discrimination despite the extension of 
the area supplied by a single neuron. 
4. The areas of the axes of the afferent fibers also increase in 
proportion to the increase of the body surface. (Table 9,B.) 
5. The growth of the large spinal cord cell bodies is compara- 
tively slight. The diameter of the fibers increases much more 
rapidly than that of the cell body, as shown by the ratios in table 
8, and in the cell body the nucleus-plasma relation is nearly 
constant within the limits of these observations (table 13). 
The enlargement of the axon to meet the requirements of the 
increased muscle mass to be innervated is therefore not accom- 
panied by any notable increase in the size or internal arrange- 
ments of the cell. 
These results reveal a marked difference, then, between the 
growth changes which take place in the afferent as contrasted 
with the efferent neurons of the first order, but it remains for 
future investigation to determine the corresponding growth 
changes in the case of the central neurons (i.e., neurons which 
lie entirely within the central system) as well as in those which 
constitute the peripheral ganglia. 
