ON THE NUMBER AND RELATIONS OF THE GANG- 

 LION CELLS AND MEDULLATED NERVE 

 FIBERS IN THE SPINAL NERVES OF FROGS 

 OF DIFFERENT AGES. 



By Irving Hardesty. 



[From the Hearst Anatomical Laboratory of the University of California). 



CONTENTS. 



I. Introduction. 



II. Material and Technique. 



III. General Results of the Enumerations. 



IV. The Number of Spinal Ganglion Cells and their Relation to the Num- 



ber of Fibers Connected with the Ganglion. 

 V. Further Observations on the Conditions Determining the Excess of Fi- 

 bers on the Distal Side of the Spinal Ganglion. 

 VI. The Gain of Cells and Fibers with the Gain in Weight. 

 VII. Summary. 

 VIII. Bibliography. 



/. Introductio7i. 



That the number of medullated nerve fibers in the spinal 

 nerves increases during the growth of the animal toward ma- 

 turity is generally accepted. Aside from the evident require- 

 ments of growth, the fact has been established on several occa- 

 sions, at least for the frog and mammal, by direct enumerations 

 of the fibers. 



In two papers of some years ago the author ('99 and '00) un- 

 dertook to determine the rate at which the increase of fibers takes 

 place in the frog. It was then found (i) that the increase occurs 

 more rapidly in younger specimens ; (2) that in specimens of 

 varying weights, counts of the fibers in transverse sections 

 taken at intervals along the ventral root toward the spinal cord 



