MULTIPLE NEUROMATA OF THE CENTRAL NERVOUS SYSTEM. 789 
play ; influences which accelerate or retard the period at which nerve fibres are brought 
into functional activity have also an effect in determining the date of complete axial 
fibril and myelin differentiation. Marcuties has pointed out that in the newly-born 
kitten, if the eyelids on one side are carefully opened, the optic nerve on that side 
myelinates before that of the opposite side excluded from the light, and numerous 
other instances might be given where the completion of differentiation is related to 
the completion of function. The fibres in the distal end of a non-united nerve remain 
for a very considerable time as embryonic nerve fibres, but when secondary suture is 
carried out they very rapidly effect a complete differentiation—in a period of time in 
which it would have been impossible for axis-cylinders to grow out from the central 
to the distal end. 
The differentiation proceeds, therefore, pari passu with the functioning which is 
its determining cause. Batitance and Stewart think that some stimulus, afforded 
by the conducting of impulses, is necessary in order to admit of the full development 
of the nerve fibres, and Granam-Kerr relates the differentiation of the neurofibrils to 
the repeated passage of impulses along them. To attain its perfect structure, therefore, 
a nerve must be brought into relation to its functional Inanspruchnahme. BETHE, at 
present the most prominent supporter of the peripherist view, claims that it is not 
necessary to have complete differentiation to have an autogenous regeneration. 
Regeneration in the distal end of a non-united nerve is not due to the ingrowing of 
axis-cylinders from the central end, but the autogenous regeneration of the sheath 
of Schwann cells forms a neurogenous tissue to which complete differentiation comes 
when the nerve is brought into its Funktionskreis. This neurogenous tissue is the 
maximum of what could be expected for the regenerative powers inherent in cells 
which have been derived from highly differentiated elements, while the first develop- 
ment is carried out in definite correlation with tissues all in the act of development. 
Brrue in some of his interpretations may have overstepped the mark, and some of his 
experiments may not be unequivocal, yet his basal contention, maintained after long 
research and in face of the severest criticism, that the new fibres arise within the 
proliferated cells of the sheath of Schwann and not as outgrowths of the central 
axis-cylinder, is supported by the results of the most recent embryological researches, 
by a very large number of workers on the regeneration of nerves, and by numerous 
observations on the genesis of nerve fibres in tumours. 
A further criticism has been raised by Casa and PERRoNcITO in regard to the 
division of the fibres and the leashes of fine fibrils found in the old neurilemma sheaths 
of a regenerated nerve. Those writers think that it is impossible to explain such 
findings except by the dissociation of the old axis-cylinder into its constituent fibrils 
and the terminal or collateral branching-off of these primitive fibrils. BaLLtancr and 
Stewart have noted that the proliferated sheath of Schwann cells divide in an 
obliquely longitudinal plane so that the resulting daughter cells somewhat overlap 
~ one another, and by successive divisions closely-set longitudinal columns or chains 
