NERVOUS SYSTEM 



105 



metrically. This method tends to give a greater value for the 

 area of the sheath and hence to reduce the relative area of the 

 axis, which was here found to be about 40 per cent of the entire 

 fiber. 



Using the cells and fibers from the localities shown hi figure 

 11 a comparison has been made between the growth of the 

 spinal ganglion cells and their fibers and the corresponding 

 ventral horn cells and their fibers at the level of the seventh 

 cervical nerve (Donaldson and Nagasaka, '18). The fibers were 

 fixed in osmic acid and the cells in Bouin's fluid. Twelve body 

 weight groups were studied. The relations found can be best 



Fig. 11 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 

 ventral root; at C, section of dorsal root. 1. The spinal ganglion, cut in longi- 

 tudinal section. 2. Transverse section of segment. 3. Plane of longitudinal 

 section of the segment. 



presented in tables 67 and 68 in which the body weight groups 

 are reduced to four. 



The ratios here given show that the increase in the diameters 

 of the fibers has been nearly the same in all three cases. The 

 increase of the spinal ganglion cells hi diameter follows that of 

 their fibers, while in the case of the ventral horn cells, the in- 

 crease is much less than that of the ventral root fibers as the 

 growth in these cells is slight after puberty. 



Thus within the limits here taken the ganglion cells continue 

 to increase in diameter with the growth of the rat, while the 

 fibers arising from them increase slightly more. 



