2i8 Joiinial of Comparative N myology and Psychology. 



mate and my own is the fact that Stilling's estimate does not 

 include the nerve fibers, the diameter of which is less than 



As we have already noticed, my results are 26.83^ greater 

 than Stilling's. The question, therefore, is to what extent 

 this difference can be accounted for by the nerve fibers in the 

 ventral roots, the diameter of which is less than 7. 5 11. 



KoLLiKER (1850) makes the statement that in the ventral 

 roots three-fourths of the fibers range from 13.5 to 24. 9 //, and the 

 small fibers are for the most part from 5.6 « to 6.8/i. 



To determine the relation between the fine and the large 

 fibers in the ventral roots of man, Siemerling (i886-'87) count- 

 ed in each root, mostly on the left side, the nerve fibers seen in 

 9 sq. mm. of the ocular micrometer (oculus 3, system 7, Hart- 

 nack). He thus counted in the ventral roots 559 fibers, the 

 diameter of which was less than 7.5 [x and 552, the diameter of 

 which was more than 7.5 a. 



In other words, the fine and large fibers were found by 

 him to be about equal in number. 



Such a small count as this must be considered, however, 

 very inadequate in the determination of a relation, subject to 

 such considerable local variations. 



./. Determination of the Fine Fibers in the Ve)itral Roots. — 

 To determine this point, the author has made counts from a 

 few fascicles of each of the ventral roots of the spinal nerves. 

 In making these counts, such fascicles were selected as had the 

 same number of nerve fibers per square mm. of the cross-section 

 as the average found for the entire root. The fibers, the diam- 

 eter of which was 7.5// or more were considered large fibers, 

 and those the diameter of which was less than 7.5 ii were con- 

 sidered small fibers. After finding what per cent of the select- 

 ed fascicles was represented by small fibers, the number of 

 small fibers in the entire root was calculated in accordance with 

 this relation. 



The results are presented in Table III. 



According to the calculations in this Table there are in the 

 ventral roots 80,747 nerve fibers the diameter of which is less 



