NERVE CELLS OF THE CRAYFISH 45 
in which the nerve impulse travels, or are they simply supporting 
structures, as Sziits (’14) has suggested? 
Das Stiitzgeriist der Nervenelemente ist ihre neurofibrillére Struktur. 
Es ist in mehreren Fallen gelungen, den innigen Zusammemhang 
zwischen der Gestalt und der neuvofibrilliren Struktur der Nervenel- 
emente nachzuweisen. Die Neurofibrillen muss man daher fiir den 
Triiger und die Stiitze der Zellgestalt und nicht fiir specifische leitende 
Elemente ansehen. 
We are in no position as yet to decide this question. There are 
two problems, however, of fundamental interest which can be 
discussed profitably: 1) Do the neurofibrillae exist in the living 
protoplasm? 2) What is their relation to the ground-substance 
of the cytoplasm? 
The first of these questions has not received the attention it 
deserves. Most observers have tacitly assumed the preexistence 
of neurofibrillae in the living protoplasm. The evidence in 
favor of it is not convincing to say the least. In 1868 Max 
Schultze, a microscopist of the most exceptional ability, un- 
hampered by any preconceptions, discovered a fibrillar structure 
in the freshly teased cells of the electric lobe of Torpedo. This, 
as we have seen (p. 43), is as favorable a material for the pur- 
pose as the large crayfish ganglion cells. Dahlgren (’15) seems 
to be the only one who has attempted to confirm this observa- 
tion. He reported ‘“‘some trace . . . . of neurofibrils”’ 
and figures a faint longitudinal striation. This object deserves 
further study with the use of vital dyes. 
M. Heidenhain was impressed with the evidence obtained by 
Cajal (’07) of the individualistic behavior of neurofibrillae in 
regenerating nerves. The fact that fibrillar differentiations 
appear after so many diverse fixations surely indicates that, 
even if they do not exist as such in life, they represent a peculiar 
type of organization in the neuroplasm so that their presence 
in a given cell is strong presumptive evidence of its nervous 
character. 
The controversy in the literature has centered about their 
morphology in fixed and stained preparations which are assumed 
to give true pictures of their forms and relations. Two categories 
