Dunn, Nerve Fibers of the Frog. 319 



As ScHWALBE finds no evidence that the nerves to the 

 extremities are more frequently innervated than those to the 

 thorax and abdomen he is by exclusion compelled to accept the 

 first hypothesis. This he proceeds to test. In the three frogs 

 chosen he finds the length of the brachial nerve to its extremity 

 as compared to the length of the ischiadicus to be approxi- 

 mately 1:2.35 (ScHWALBE, 1882, p. 21); that is, if there were a 

 direct relation, the ratio between the squares of the diameters 

 of the nerve fibers in these localities should correspond to that 

 for their length and be 1:2.35, but their ratio is much less, 

 being in the most favorable case, 1:1.5. 



Instead of admitting, therefore, that the relation does not 

 hold, ScHWALBE prefers to assume that the general relation 

 is true but is modified by some other factor. He assumes, 

 then, that some other influence is working to render the cali- 

 ber of the nerve fibers in the brachial nerve greater than it 

 should be in proportion to the length of the nerve. 



Moreover he emphasizes the fact (p. 24) that these re- 

 marks refer to the sections of the spinal nerves nearest the 

 spinal cord and that in their further course these fibers are mod- 

 fied, that is to say, reduced in diameter. 



He then proceeds to explain in accordance with his theory 

 what must be the meaning of a nerve containing fibers differing 

 greatly in diameter, and states that the smallest fibers must be 

 given off in the branches nearest the spinal cord. It is to be 

 noted that Schwalbe has no observations to confirm this view. 



During the course of the present study the attempt was 

 made to ascertain the destination of the very large fibers in the 

 sciatic nerve. To this end measurements of the nerve fibers 

 were taken at the levels at which the fibers had been enumer- 

 ated. These levels are shown in Figure 2 and fully explained 

 in Section B, Number of Nerve Fibers, page 310. 



These two lines of investigation were followed: first, a 

 determination of the average area for each nerve fiber at the 

 various levels; second, a determination of the absolute measure- 

 ments of the largest nerve fibers at the same levels, and in the 

 branches. 



