REGENERATION OF PERIPHERAL NERVES 487 



mately the normal number of fibers for the middle zone of the 

 peroneal nerve of the albino rat with a body weight of 135 grams 

 and belonging to the strain here used. 



Referring again to table 1, we observe that no. 224 weighed 

 104 grams, no. 223 weighed 117 grams and no. 222 weighed 182 

 grams or 75 per cent more than no. 224. The average of the 

 three fiber counts of no. 224 is 2250, the average of no. 223 is 

 2312 and the average of no. 222 is 2325 or an increase of about 

 3.5 per cent over the average of no. 224. In this series, there- 

 fore, the heavier animal has the greater number of medullated 

 fibers. 



Taking body weight as a rough index of age, we note that 

 there is a constant increase in the number of fibers as the ani- 

 mal grows older. With an increase of 75 per cent in body weight 

 we find an increase of about 3.5 per cent in the number of fibers 

 in the peroneal nerve. This observation must be held to apply 

 to young or developing animals for Dunn ('11) has shown that 

 old animals lose fibers. 



Summarizing the observations on the normal peroneal nerve 

 we may state that: In an animal of 135 grams body weight the 

 middle zone of t'he peroneal nerve contains about 2306 fibers; 

 the number is the same for each side; in a developing animal 

 an increase in the number of fibers accompanies increase in body 

 weight or advancing age; in the 10 mm. of nerve used in this 

 series there is an increase of about 1.5 per cent in the number 

 of fibers as we pass from the proximal to the distal end. Dunn 

 ('02) has shown that in the frog there is an increase in the number 

 of fibers between the sciatic trunk and its two distal divisions 

 of about 5 per cent, due to branching. 



NUMBER OF FIBERS ON THE CONTROL SIDE OF OPERATED ANIMALS 



Having examined the numerical relations in the peroneal nerve 

 of the normal animal we will next examine the control (left) 

 side of our operated animals. 



Table 3 presents the data from Series 2, all of which are oper- 

 ated animals. In this table the data are arranged according 

 to the age of the animal at the time of killing. 



