Differentiation of Neuroblasts 35 
question were adopted. First the cells of the antero-lateral part 
of the ventral horn, this being the region affected, beginning with 
the section on which the 12th ganglion appears, and going to the 
section on which the 15th appears, were counted on each side. 
There is evidently much chance for error in this, particularly as 
the sections were not cut with this in view, and a change of focus 
brought different cells into the visual field, but the cells of each 
section were always counted a number of times, and the probability 
of error is equally great for each side. While, therefore, the figures 
obtained probably do not represent the actual number of cells, I 
think they may be regarded as giving a fairly accurate compari- 
son of the two sides. ‘The total loss for the whole area was 50 
- per cent, and this was distributed to the three nerves as follows: 
PER CENT 
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SH RORBacsoasd sonsocense 6 sonoh oD pec bES de Dednde Tebeu reo abr analkoscbeacass sat 53-2 
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Many cells of successive sections, both in this and other specimens, 
were then measured with the ocular micrometer, and camera lucida 
drawings were also made and the dimensions taken, and while 
it was possible to demonstrate a difference in the size of the cells, 
the larger were found to be as often on the operated as on the 
unoperated side, and no abnormally small or otherwise defective 
cells could be demonstrated. Both methods of estimation, there- 
fore, seem to indicate conclusively that the loss is in the number of 
cells. 
The loss in the posterior horn is less, but still evident. Measure- 
ments showed that the distance from 4 to B (Fig. 14) is always less 
on the injured side and also that the distance from the center to the 
periphery in the dorsal part of the cord is slightly decreased. 
A quantitative estimate of this difference seemed impracticable. 
Experiment 206. The period of incubation before operation 
was 3 days 1 hour. The wing, a small elevation as in experiment 
538. The right wing was again removed, and the embryo pre- 
served five days later, so that when examined it was 8 days I 
hour old. A slight thickening only was visible in the region of the 
