REGENERATION OF PERIPHERAL NERVES 



489 



If we divide these records into age groups, as is done in table 

 3, we find that five such groups are formed, namely: a 65-day 

 group, a 128-129-day group, a 156-166-day group, a 193-day 

 group and a 276-day group. For the 65-day and the 193-day 

 groups only one entry is available, these, therefore, may be ex- 

 cluded. Owing to the failure of the 166-day animal (no. 100) 

 to gain in weight, this will be omitted in the discussion, since 

 it may be safely assumed that whatever has interfered with the 

 growth of the animal has also modified the regeneration process. 



This leaves for comparison the 128-129-day group with 5 

 entries, the 156-164-day group with 7 entries and the 276-day 

 group with 3 entries. Bringing the averages of these groups 

 together in tabular form we have the following: 



The average number of fibers in the control nerves of each of 

 these groups is respectively 1981, 2025 and 2083. This indicates 

 a steady increase in the number of medullated fibers with advanc- 

 ing age, the interval being 147 days between 129 and 276 days 

 of age. The difference in number of fibers between the extremes 

 is 102 or about 5 per cent of the smallest number. 



Comparing the averages of these .three groups with the records 

 of normal unoperated animals, as presented in table 1, we ob- 

 serve that the averages of operated animals fall below the counts 

 of even our lightest unoperated animal no. 224.* 



Taking 2306 as our estimated number of fibers for the middle 

 zone of an unoperated animal of 135 grams body weight and 

 comparing this number with the number of fibers (1937) found in 

 the control nerve of operated animal no. 113 of 140 grams body 



