DIAMETERS OF NERVE CELLS AND FIBERS 531 
To obtain all the data desired, two rats of like age and size 
were required. From the left side of one, the two spinal roots, 
the ganglion, and a short part of the nerve were removed together. 
These were extended to the normal length on a bit of cardboard 
and fixed for twenty-four hours in 1 per cent osmic acid. From 
the same rat the seventh cervical segment, with the right roots, 
ganglion, and nerve attached, was removed and fixed in Bouin’s 
fluid for twenty-four hours, according to the procedure de- 
seribed by Sugita (17). 
Fig. 1 A scheme of the seventh cervical segment of the spinal cord. Levels 
of the nerve-fiber sections: At A, section of seventh nerve; at B, section of ven- 
tral root; at C, section of dorsal root. 1. The spinal ganglion, cut in longitudinal 
section. 2. Transverse section of segment. 3. Plane of longitudinal section of 
the segment. 
From the second rat of the pair the seventh cervical segment 
of the cord, without the nerve roots, was removed and fixed also 
in Bouin’s fluid. The nerve roots and nerve fixed in osmic acid 
were washed for twelve hours, run through the alcohols, cleared 
in xylol, rapidly imbedded in paraffin and cut in sections 8u 
thick. The piece of the spinal cord with the ganglion from 
the first rat and the piece of cord from the second rat, both 
of which had been fixed in Bouin’s solution, were washed for five 
minutes in running water, then treated as above, cut in sections 
12u thick and stained with thionin. 
Figure 1 shows the localities at which the six series of sections 
were made. . 
