a 
340 | FLEXNER. [VoL. XIV. 
tion was effected. At the end of the first twelve hours 
and about equally at the conclusion of eighteen hours, active 
cell proliferation in the divided end is going on. The evi- 
dences for this are found in the rich mitosis encountered as 
well as in the accumulation of small, immature cells at the 
injured extremity. The most active division is found in the 
tissues immediately adjacent to the epidermal elements close 
to the superficial epithelial cells and to a far less extent in the 
cells at a distance (Fig. 2). The surface epithelial epidermal 
elements show no evidence whatever of mitosis; while close 
to the site of operation degenerative changes, consisting of 
fragmentation of cell nuclei (karyorhexis), are to be made out. 
Although especial attention was directed to the ganglion cells 
in the nerve cords at this time, mitotic figures were never 
demonstrated in them. 
The new cells accumulate about the cut end and quickly 
cover over the defect. At the end of twelve hours they have 
pushed forward to the extremity, have become continuous with 
the intact epidermal cells, and have already formed a covering 
for the denuded structures (Fig. 3). Whether an embryonic 
form of epidermis or not, considerable masses of multi- 
nucleated protoplasm (syncytium) form the outermost layer of 
new cells. 
At the end of twenty-four hours cell division in the regen- 
erating end is quite over. Long and painstaking search is 
required to discover a single karyokinetic figure. But the 
cellular accumulation is now considerable. The new cells not 
only cover in the defect and are evident to the naked eye as a 
projecting white point, but they surround and inclose the 
divided nerve cords. The changes noted at the end of forty- 
eight hours consist in a somewhat more orderly arrangement 
of these cells about the cord and the invasion by them toa 
small extent of the bundle of fibrils themselves (Fig. 4). 
The completed ganglion is found at about the sixtieth hour 
(Woods Holl temperature), although at this time the cephalic 
extremity does not appear to have attained its maximum size 
and the regenerated epidermis is still unpigmented. It may 
happen that in the ganglia at this time there is an undue rich- 
