530 S. WALTER RANSON 
less irregular manner, run, for the most part, in a general direc- 
tion from center (c) to periphery (p). This predominant direc- 
tion is due to the chemiotactic influence exerted upon the grow- 
ing fibers by the distal stump. There are in the field three 
branching fibers (a). Notice that in each case the centrally 
directed limb of the Y is the thickest fiber, while the two periph- 
erally directed limbs are thinner, and represent the branches. 
Had these fibers arisen in situ, the branching fibers would in 
themselves be difficult to account for; but the fact that the 
central limb of the Y is almost always the largest of the three 
would be even harder to explain. There are no end bulbs repre- 
sented in the drawing, and in fact there are few in this region. 
This is the oldest portion of the nerve plexus in the scar and the 
fibers are already of great length and few can be seen having 
a true termination within the thickness of a section. As one 
approaches the distal extremity of this plexus, 9 to 13 mm. 
from the central stump, these end bulbs become relatively much 
more numerous, since we are dealing here with the growing 
ends of the fibers. Often in the place of an end bulb one sees 
the end of a fiber breaking up into a large number of fine branches. 
It is an interesting fact that the farther distally in the scar the 
plexus goes the more parallel its fibers become, and the more 
directly they run toward the distal stump. This is explained 
by the fact that the earliest fibers penetrate the scar at a time 
when the distal stump has not undergone the alteration neces- 
sary for the exercise of the chemiotactic influence and their 
direction is very irregular. These early fibers by stereotropism 
govern the direction of the bundles. On the other hand, the 
early fibers in the distal portion of the plexus are from the first 
under the chemiotactic influence of the distal stump which is 
stronger because of the proximity of the distal stump. 
Dog vu, killed thirty-four days after the operation, serves 
as a good illustration of a scar when the two ends of the nerve 
have been sutured. The suturing was not well done and a gap 
of some size between the two stumps was filled with scar tissue. 
Into this scar the fibers from the central stump can be followed. 
The fiber plexus in the scar is very much like that in Dog x. 
