Hatai, Ganglion Cells in the Rat. 1 1 5 



the spinal ganglion with the number of fibers in the dorsal nerve 

 root, have found a more or less striking excess of cells in the 

 ganglion. 



So far as I am aware, no investigators have ever enumerated 

 the number of the spinal nerve fibers in any mammalian from 

 the period just after birth to maturity. The following table 

 shows the total number of the dorsal root fibers in the roots be- 

 longing to to the selected ganglia. 



TABLE IV. 



Showing the Total Number of the Dorsal Root- Fibers at Different 

 Ages in the White Rat. 

 Body-Weight 



Grams. VI Cervical. IV Thoracic. II Lumbar. 



From the Table IV it is clear that at any given age the 

 total number of the fibers differs in the three roots of the same 

 animal. It is also shown that the number of the fibers is 

 greatest in the cervical region and that the numbers in the 

 lumbar and thoracic regions follow in order named, except in the 

 case of the 68. 5 gram rat, where the number of the fibers is 

 greater in the thoracic than in the lumbar nerve. Taking the 

 number of the fibers in the thoracic as a standard (167 grams), 

 the following ratios are obtained : Thoracic I, lumbar 1.07, 

 cervical 2.9. Briefly stated, the total number of the dorsal 

 root fibers in the VI cervical nerve at 167 grams is approx- 

 imately three times as great as in the case of either the 

 thoracic or lumbar at the same age. 



The observations of Birge ('88) and Hardesty ('99) on the 

 frog show an excess of the dorsal root fibers in both cervical 

 and lumbar enlargements, and estimates made by Stilling of 

 the area of the cross-section of the dorsal roots in man, show 

 the same thiuCT. 



1 These figures were obtained from a rat having a body-weight of 69 grams 

 and not from the one weighing 68.5 grams, the cervical ganglion of which was 

 alone counted. 



