ON THE INCREASE IN THE NUMBER OF MEDUL- 
PED NERVE oPIBERS IN THE “VENTRAL 
ROOTS OF THE SPINAL NERVES OF THE GROW- 
ING WHITE RAT. 
By SHINKISHI Hartat. 
(from the Neurological Laboratory of the University of Chicago) 
This investigation is a continuation of previous work (’02) 
on the medullated fibers in the dorsal roots of the spinal nerves. 
The following results were obtained from the earlier investi- 
gation: 
The spinal ganglia of the white rat were found to contain 
two kinds of cells which are differently characterized. One 
kind is of large size, while the other is much smaller. From 
the histological evidence, the larger cells were regarded as the 
adult functional form, while the smaller were considered to be 
the cells in a developing stage (’o1). 
If this view is correct and if the total number of cells in 
the ganglion remains the same throughout life, then we should 
expect more of the large cells in the ganglion of the adult 
than in that of the young animal. The converse should also 
be true; the younger animal should have more of the smaller 
cells in the ganglia. By counting the ganglion cells in animals 
of different ages, this hypothesis can be tested. According to 
BUHLER (’98), the large functional cells are constantly degen- 
erating, and the smaller cells which are developing take their 
place. If his view were true, the spinal ganglion cells should 
decrease in number as the animal gets older, since it is believed 
that in the rat the ganglion cells never divide after the first 
days of extra-uterine life. BiHLEer’s hypothesis, therefore, 
can be tested by an enumeration of the total number of the 
spinal ganglion cells at different ages. For these two reasons, 
I undertook this investigation. 
