36 JouRNAL OF COMPARATIVE NEUROLOGY. 
clear space, or centrosphere, which surrounds the centrosome 
shows a definite figure in young cells. The structures above 
mentioned, however, are not to be seen when the cell attains a 
mature stage, and the radial arrangement of the protoplasm 
within the centrosphere not only becomes invisible, but the clear 
area, or centrosphere itself, also is dimished more or less in its 
diameter. In some cases, the radial arrangement of the proto- 
plasm in the region of the plasmosphere is entirely absent (Fig. 
11). These structural differences between an adult and young 
stage signify, no doubt, the slow atrophy of the sphere. If 
my statement is true, we can hardly imagine that the centro- 
some which is in process of degeneration may undergo division 
in a normal condition. The writer has examined a large num- 
ber of the nerve cells of the white rat in which the centrosome 
is nicely demonstrable but has not noticed even a slight trace of 
the process of division. 
These observations raise the whole question of the division 
of mature nerve cells. 
The current theory claims that after a nerve cell once sends 
out its axis cylinder it is incapable of division or further repro- 
duction. It is known, however, in the case of another kind 
of tissues, that under a certain pathological condition the ma- 
tured cells produce daughter cells by the dividing process, either 
mitotic or amitotic. This phenomenon has been reported in the 
nerve cells also, but in our opinion the results are not fully 
established. TrEprEscui' who studied the results of intoxication 
on the mammalian body has observed the presence of karyo- 
kinetic division in the adult nerve cells. According to him this 
phenomenon occurs three days after the poisonous substance 
has been introduced into the body. Later Nexis’ suggested 
the possibility of the division of an adult nerve cells under the 
1 TEDESCHI, 4.—Anatomische-pathologische und experimentelle Unter- 
suchungen iiber die Regeneration des Nerven Gewebes. Vergl. Mith. Centraibl. 
f. allg. path. u. path, Anat., Jena, Bd. viii (’96), p.,449-451. Also Anatomische 
experimentellen Beitrige zum Studien der Regeneration des Gewebe des Cen- 
tralnervensystem, Aeitr. 2. path. anat. u.z. all. path., Jena, ’97, Vol. xxi, p- 43-72. 
1 NELIS, C.—Loc. cit. 
ee 
