AUTHORS’ ABSTRACT OF THIS PAPER 
ISSUED BY THE BIBLIOGRAPHIC SERVICE 
ON THE INCREASE IN THE DIAMETERS OF NERVE- 
CELL BODIES AND OF THE FIBERS ARISING 
FROM. THEM--DURING THE *LATER 
PHASES OF GROWTH (ALBINO RAT) 
HENRY H. DONALDSON AND G. NAGASAKA 
The Wistar Institute of Anatomy and Biology 
THREE CHARTS AND ONE FIGURE 
In the later phases of growth some neurons increase not only 
in the diameter of the cell body, but also in the diameter of the 
fiber or fibers growing from the cell body. Moreover, in the 
case of the fiber, the increase occurs not only in the diameter of 
the axis cylinder, but, when myelinated, in the myelin sheath 
also. 
In order to determine more precisely how this increase in 
diameter is distributed between the cell body and the fiber 
coming from it, we have undertaken to observe during the later 
phases of growth what takes place in two classes of neurons at the 
level of the seventh cervical segment of the spinal cord of the 
albino rat. 
The neurons chosen for study were a) those with the largest 
cell bodies in the ventro-lateral group of the ventral horn and the 
ventral root fibers which were assumed to come from them, and, 
b) those with the largest cell bodies in the corresponding spinal 
ganglion together with the largest fibers in both the dorsal root 
and in the nerve just distal to the ganglion. This seventh seg- 
ment of the spinal cord with ganglia and roots was removed from 
a series of twenty-four male albino rats which are listed in table 1. 
As table 1 shows, these rats range from 17 to 360 days in age 
and from 18.7 to 316.3 grams in body weight. 
As one object of the study was to determine whether the nerve 
fibers continued to increase in diameter after the cell bodies had 
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