Dunn, Nerve Fibers of tlie Fmg. 309 



In the employment of either method special effort was 

 made to include the very small medullated fibers which, under 

 ordinary circumstances, elude observation. 



b. Detetmination of average areas for^ each fiber. The 

 determination of areas was made b}' the aid of camera lucida 

 drawings of the selected sections. In the execution of these 

 drawings all of the nerve sheath wss excluded and the outline 

 was made to follow the periphery of the nerve fibers, thus in- 

 cluding only the fibers themselves and the spaces lying between 

 them. The area included by the outline of this camera draw- 

 ing was determined by planimetric measurement and the diam- 

 eter by a millimeter scale. The accuracy of this diameter 

 measurement was tested by actual measurement upon Ihie sec- 

 tion itself From these data the Uw^ area of the section was 

 computed. 



The average area for each ner-v e fiber was determined by 

 dividing this true area expressed in square micra by the num- 

 ber of fibers contained in the section. 



For any section in which spreading had occurred, the per- 

 centage of added space was determined by a special method- 

 The section was photographed and on the print the additional 

 space was lightly outlined in pencil. By carrying the plani- 

 meter along the pencil line the added area was measured. Tlie 

 portion of the entire area of the photographed nerve which 

 this included area covered gave the percentage to be deducted 

 from the former computed area of the nerve. 



c. Determination of the average area of the largest fibers. 

 Confirmatory measurements were made upon the largest fibers 

 at the several levels. For each of fhe??e fibers the mean ^f 

 two diameters was obtained, and from this mean the area of the 

 selected fibers was computed. 



' The area for the fiber is an average ai ea detcimined by dividing the 

 area of the nerve trunk by the number of nerve fibers of which it iscomposed, 

 while the area, of the fiber is determined by measurements made upon iTie 

 fiber alone. The distinction made in this and the following section between 

 the area /cr the fiber and the area of the fiber j.s maintained throughout Ibe 

 discussion, and the italicised words require this difference in interpretation 

 wherever they are introduced. 



