OUTGROWTH OF THE NERVE FIBER 
821 
seen that during the time in which it was under observation, new 
processes or pseudopodia were formed and some present at first 
were withdrawn. The movement of the end was 44^ during the 
47 minutes in which it was observed. This is at the rate of .94/x 
per minute or 56^ per hour, which is the most rapid extension 
that I have ever observed. This is all the more remarkable 
because of the great length of the fiber, for one would naturally 
expect a gradual lessening of the activity as the limit of growth is 
approached. There can be no doubt that the red blood corpuscle 
was a stationary point. Its position with reference to five other 
corpuscles remained fixed throughout the period of observation, 
and even on setting the preparation on edge, i.e., turning it 90", 
no change in relative position was observed, although the plasma 
in the meshes of the clot flowed perceptibly. The direction of 
growth of the fiber served, however, to draw the fiber close to 
the corpuscle. One feature shown in the present case and ob- 
served also in a number of others, was the formation of processes 
of considerable thickness and length which were afterward with- 
drawn (text fig. 3), indicating that the movement of the end is 
not directed constantly toward a particular goal."^^ 
As already mentioned, the fibers that are found in preparations 
of the nervous system usually proceed from masses of cells so 
opaque that their exact mode of origin cannot be determined. 
Fibers whose origin could be seen in single cells have been observed 
a number of times and several are shown in figs. 18 and 20. Fig. 
18 differs from the others in so far as the cell itself has wandered 
out from the mass, remaining connected with the latter by a long 
filament (6) about 300// long. The hyaline process (a) at the 
distal end of the cell is relatively short. 
This leads to the consideration of the formation of protoplasmic 
fibers by the drawing apart of cells. Fig. 19 shows a bipolar cell 
the processes of which were formed in this way. They are 
tightly stretched and at both ends terminate in masses of cells, 
so that it is not possible to make out their exact mode of termina- 
" This is akin to what Held has termed "Prinzip der Auswahl" for which he has 
adduced evidence (Op. cil., p. 270). 
