596 



THE NERVE CELL. 



Others, such as Flemming, 1 Lugaro, 2 Dogiel, 3 Levi, 4 Cox, 5 Mann, and 

 Bethe, 7 have, on the other hand, insisted upon the existence of fibrils, 

 distinct from the reticulum, running through the protoplasm from and 

 into the several processes, and this view is now generally held, and has 



been adopted even by those who 

 until quite lately were of the 

 opposite opinion. 



While it is easy, by certain 

 methods and in certain cells, to 

 show a fibrillation both in the cell 

 body and in its processes, with 

 other cells it is more difficult on 

 account of the complexity of course 

 of the fibrils within them. The 

 axis cylinder of a nerve is an 

 especially favourable object for the 

 observation of nerve fibrils, and they 

 become naturally dissociated at the 

 e P termination of nerves, where in some 

 cases, as in the cornea, the axis 

 cylinders break up into pencils of 

 fibrils. It must be noted that these 

 terminal fibrils are almost invariably 

 branched, and sometimes even form 

 a network; which appears to indi- 

 cate that there may be lateral com- 

 munications between them, and that 

 they may not be always entirely dis- 

 tinct even throughout their course 

 in the nerve fibre. 8 Such lateral com- 

 munications are sometimes apparent 

 in the fibrillations of the dendrons, 

 as well as in those of the cell body, 

 and although less obvious in the 

 course of the axis cylinder process, 

 they may not be altogether absent 

 in this. Nor are there any physio- 



A. B. 



Fig. 302. — Nerve cells of Hirudo. — A, Unipolar 

 motor nerve cell ; a, network of neuro- 

 fibrils in cell body near surface ; b, net- 

 work near nucleus, n ; c, afferent neuro- 

 fibrils ; d, efferent neuro-fibril. B, Sen- 

 sory nerve cell, bipolar ; a, body of cell ; 

 n, nucleus. A neuro-fibril is seen passing 

 from its ramification between the epi- 

 dermis cells, ep, close to the cuticle, en, 

 to form a network within the nerve cell, 

 before passing on to the central nervous 

 system. — Apathy. 



logical facts which would lead to the belief that nervous impulses are con- 

 ducted within the nervous units by isolated fibrillar 



The question of the existence or non-existence of fibrilke may 

 be now regarded as having been settled by the discovery by Apathy 9 

 of definite fibrils, entirely different from any spongioplastic reticulum, 

 in the nerve cells of annelids. The fibrils form a network with com- 



1 Beitr. z. Anat. u. Embryol. als Festgabe J. Henlc, Bonn, 1882 ; Arch. f. mikr. Anat., 

 Bonn, 1895, Bd. xlvi. S. 379 ; Arch. f. Psychiat., Berlin, 1897, Bd. xxix. 



2 Riv. dipatol. nerv., Firenze, 1896. 



3 Arch.f. mikr. Anat., Bonn, 1893, Bd. xli. S. 62 ; Anat. Anz., Jena, 1897 ; Monthly 

 Internal. Journ. Anat. and Physiol., 1897. 



4 Riv. dipatol. nerv., Firenze, 1897. 



5 Monthly Internat. Journ. Anat. and Physiol., 1898, vol. xv. p. 209. 



6 Journ. Anat. and Physiol., London, 1894, vol. xxix.; and Verhandl. d. anat. Gesellsch., 

 Jena, 1898, Bd. xii. S. 39. 



7 Verhandl. d. anat. Gesellsch., Jena, 1898, Bd. xii. S. 39 ; Morphol. Arb., Jena, 1898, 

 Bd. viii. S. 95. 



8 Cf. G. Retzius, Biol. Fbren. Forhandl. Verhandl. d. biol. Ver. in Stockholm, 1898, fc>. 83. 



9 Mitth. a. d. zool. Station zu Neapel, Leipzig, 1897, Bd. xii. 



