464 THE AMERICAN NATURALIST. [Vor. XXXIV. 
opportunity of testing the theory. It has long been known 
that when a nerve is cut or a bundle of fibres in a central 
organ injured, some fibres degenerate in one direction, some 
in another. The question naturally arises, do these degenera- 
tions take place in accordance with the assumed cellular nature 
of the neurone? 
Experiments upon large protozoans have shown that when 
these unicellular animals are cut in two so that one part, which 
may be the smaller, contains all the nucleus and the other is 
without even a fragment of this organ, the part without the 
nucleus invariably soon dies, while that. which retained the 
nucleus may regenerate the lost part and continue to live. 
The nucleus is in some way absolutely essential to the con- 
tinued life of the cell. 
The same is true of nerve fibres. If a nerve be cut, that 
portion of each fibre which is thus severed from the nucleus- 
bearing part, the so-called ganglion cell, invariably dies, even 
though it remains among the tissues of the body and is bathed 
in the fluids that are presumed to nourish it. This rule holds 
for all the degenerations of the nervous organs; after sever- 
ance the non-nucleated portions of the neurones degenerate 
precisely as the non-nucleated portion of the protozoan body 
degenerates. The degeneration of nerve fibres then takes 
place in accordance with the conception of the neurone as a 
single cell. 
Precisely as the. nucleated portion of the divided protozoan 
body continues to live and may regenerate its lost parts, so the 
nucleated portion of the neurone remains alive, and, if the 
injury has not been too severe, may reéstablish itself by throw- 
ing out new axis cylinders from the cut end of the old one, and 
thus new fibres may by growth reéstablish many of the former 
connections. Regeneration in the neurone, as in the protozoan 
cell, takes place from the nucleated part ; and this phenomenon, 
as well as that of degeneration, points very clearly to the con- 
clusion that the nucleus of the neurone, like that of any other 
cell, is a center on which the life of even the most remote 
portion of the cell is dependent. 
This conclusion leads us directly to an important interpre- 
