Dunn, MeduUated Nerve Fibers. 715 



eliminating the efferent fibers, it appears that among the afferent nerve 

 fibers the greatest number of nerve fibers of uniform size pass to the 

 muscles. 



All the findings in this study regarding the size of the medullated 

 nerve fibers point to a fundamental uniformity underlying their dis- 

 tribution. The probabilities seem to lie between two alternatives. 

 Either, first, a difference of function must be correlated with size; 

 this might be possible among the cutaneous nerve fibers where a 

 greater variation in size is coexistent with the need for transmission 

 of various cutaneous sensations. Or, second, size may depend upon 

 the amount of tissue to be innervated by the single fiber. Some pre- 

 liminary measurements still unpublished seem to show that in the 

 case of the medullated efferent fibers a direct relation exists between 

 the diameter of the muscle fiber and that of the nerve fiber by which 

 it is innervated. 



Herrick, 1902, in discussing the significance of the size of nerve 

 fibers in fishes, states, page 333, "that each functional system of 

 peripheral nerves has tolerably definite fiber characteristics, the basis 

 for which is unknowm ; that these characteristics are by no means 

 invariable, but that fibers of a given system may show considerable 

 differences in caliber and medullation in a single animal, and that 

 some of these differences, at least, can be correlated with the degree 

 of functional development of the peripheral end-organ." 



Johnston, 1908, has a very suggestive paper on the significance 

 of the caliber of the parts of the neurone in which he points out the 

 extreme differences in size in the non-medullated nerve fibers of the 

 lamprey. 



A further discussion of the literature cannot be made at this time, 

 but it is hoped that an accumulation of findings may make possible 

 a later discussion of the caliber of the medullated nerve fiber in the 

 leopard frog. 



It has been shown, Dunn, 1902, that the largest medullated nerve 

 fibers passing to the leg of the frog are not found di levels below the 

 thigh but appear in the primary branches to the thigh. This finding 

 discredited the theory of Schwalbe that the largest nerve fibers run 

 th' longest distance. 



