3i8 Journal of Comparative Neurology. 



C. Diameter of the Nerve Fibers. 



I. Introduction. 



We propose to consider at this point whether the destina- 

 tion of a nerve fiber in the frog's leg can be inferred from its 

 caliber. The law of Schwalbe (Schwalbe 1882), to which ref- 

 erence has already been make, sets forth the view that the 

 largest fibers run the longest distance. The researches upon 

 which this theory is based were carried on some twenty years 

 ago, having been published in 1882. Schwalbe based his 

 observations on a study of the dorsal and ventral roots of the 

 spinal nerves in Rana esculenta. His technique consisted of 

 macerating the entire nerve root in 20 % nitric acid at 40° C, 

 and washing once in a large amount of water, or of hardening 

 and staining in i c^ osmic acid for twenty-four hours, washing 

 and macerating in glycerine, acidulated with i % of hydro- 

 chloric acid commercial strength, for 24 hours at 40° C (Dunn, 

 1900, p. 13). The nerve tissue thus prepared was then teased, 

 and transverse measurements were made of the selected fibers. 

 The average number of measurements for each root was twenty 

 (Schwalbe, p. 11). From these measurements he constructs a 

 table showing first the average thickness, and next the thickness 

 of fibers of greatest frequency. Now, when the corresponding 

 curves from the ventral and dorsal roots are plotted it appears 

 that in the cervical region the fibers of the second nerve have 

 the largest average diameter, and in the lumbar region those of 

 the eighth nerve. Finding these largest fibers present in the 

 roots distributed to the fore and the hind leg respectively, he asks 

 the question on page twenty, "Was liegtnun aber naher, als die 

 starkeren Kaliber in den Wurzeln der Extremitatennerven mit 

 der grosseren Lange der betreffenden Nervenstrecke in Zusam- 

 menhang zu bringen ! Wollte man diese natiirlichste Auffas- 

 sung nicht acceptiren, so wiisste ich nur eine Moglichkeit der 

 Deutung jener Unterschiede. Man konnte namlich der Meinung 

 sein, dass die Extremitatennerven haufiger innervirt wiirden, 

 als die Nerven des Brust- und Bauchumfanges, und in Folge 

 dieses haufisJeren Gebrauches sich starker entwickelt hatten." 



