Ranson, /2bers in Lestons of the Brain. 197 
medial side is to be seen at a corresponding level in the normal 
brain. It happened that the knife passed along the line that 
forms the lateral limit of the medial area of dense fibers, and 
the presence of a band of scar tissue almost devoid of fibers 
enhances the contrast to some extent. 
The light band which marks the path of the knife is al- 
most devoid of fibers; but a few isolated ones may be dis- 
tinguished in the scar. Although clearly visible in the original 
preparation, they do not appear in the photograph which was 
taken with a very low power. In order to show these more 
accurately than could be done by a drawing on a small scale, a 
camera lucida tracing has been made (Fig. 5.). This tracing 
was taken from the same preparation that was used for the 
photograph, and represents a point in the lesion one-third of 
the way from the corpus callosum to the surface of the cortex. 
This preparation is No. 27 inaseries of 45 passing through this 
wound; it is therefore at some distance from either the anterior 
or posterior extremity of the lesion. These new formed fibers 
follow a very irregular course, so that it is not possible to trace 
them far in the plane of any one section. But in a number of 
cases it is possible to follow single fibers from the normal brain 
substance on one side through the scar tissue and into the nor- 
mal brain substance on the other side. Such a fiber is seen in 
oes 
Thus two tests were rigorously applied before the conclu- 
sion was formed that the fibers in the scar were really new 
elements; Ist, The fiber in question must pass completely 
across the lesion, making connections with the brain tissue on 
both sides; and 2nd, The fiber must cross near the geometric 
center of the lesion. Fibers that passed into the scar and then 
back again into the brain substance on the side from which 
they emerged were not counted as new-formed, for these might 
have been displaced into the opening left by the’ knife. One 
could not be sure that they had been formed since the opera- 
tion. Fibers that passed across the lesion near its anterior or 
posterior extremities or near its lower limit were also disre- 
garded; for these might have been uninjured fibers crowded 
