594 THE NERVE CELL. 



ive of their number, length, complexity, character, and position, forms 

 a distinct unit, which is believed, as the result of the employment of 

 the chromate of silver methods introduced by Golgi, to have no struc- 

 tural continuity with any other unit. This " theory of isolated units," 

 which is often spoken of as the " neurone * theory," from the name 

 " Neuron " having been applied by Waldeyer 2 to the nerve cell as above 

 defined (including all its processes), is not conclusively proved, nor is 

 it accepted by some prominent histologists, including Golgi himself. 

 But it is supported by the anatomical observations which have just 

 been referred to, and is found to fit in with many known physiological 

 facts, and to lend itself better than the " continuity theory " of nervous 

 elements, which it has in large measure supplanted, to the explanation 

 of phenomena which were previously obscure ; on this account it has 

 been widely adopted by neurologists, many of whom, following the 

 example of Waldeyer, habitually speak of nerve cells as neurones, 

 although the term is quite synonymous with " nerve cell " ; nor has the 

 newer name any advantage either on the score of brevity or of 

 etymology over the older and more general expression. Strong reasons, 

 moreover, as will presently appear, have lately been urged against the 

 acceptance of the theory which is associated with the newer name, so 

 that it would seem wiser to retain the term " nerve cell." The practice 

 of restricting the use of " nerve cell " to the body of the cell (" peri- 

 karyon " of some writers) should for obvious reasons be dropped. 



Structure of nerve cells. The structure of nerve cells has of late 

 years been the subject of numerous researches. 3 The general result of 

 these may be shortly given as follows : The nucleus of the nerve cell 

 is characterised by its large size, and the fact that its chromatin is in 

 relatively small amount, except in the nucleolus, which is large. 4 The 

 protoplasm of the cell body resembles that of other cells in exhibiting a 

 reticular or sponge-like structure (spongioplasm), with a clear or finely 

 granular substance (hyaloplasm) in its meshes. 5 But there are two points 

 in which it is peculiar. One consists in the occurrence of fibrils which 

 run through the protoplasm. Such fibrils were observed by Max Schultze, 6 

 who found them in both fresh and osmic preparations of nerve cells 

 (Fig. 301), and described them as passing into and out of the cell by 

 its processes, and as having the same finely varicose character as the 

 fibrils which he had also found in the axis cylinder and its terminations. 

 Of late years there has been shown a tendency to doubt the existence 

 of such fibrils, as structures distinct from the general reticulum of 

 the protoplasm. For it is obvious that the elongation of the meshes 

 of a reticulum in definite directions might simulate fibrils, as indeed 

 is probably the case in many elongated cells, such as columnar 

 epithelium, and smooth muscle. This view of the matter was taken 



1 Often erroneously written "neuron." Gr. 



2 Deutsche vied. Wchnschr., Leipzig, 1891. 



3 A concise account of these researches, with very full bibliography, is given by W. 

 Ford Robertson in Brain, London, 1899, vol. xxii. pp. 203-327. 



4 The structure of the nucleus is dealt with by Levi in various papers in the Riv. di 

 patol. nerv., Firenze, for 1896, 1897, and 1898. 



5 Like other cells, it contains a centrosome (v. Lenhossek, Arch. f. mikr. Anat., Bonn, 

 1895, Bd. xlv. S. 345). The protoplasm (interfibrillar substance) of the axis cylinder is 

 somewhat different chemically as shown by its reaction to certain stains and to osmic 

 acid from the protoplasm of the cell-body and dendrons (Monckeberg and Bethe, ibid., 

 1899, Bd. xliv. S. 135). 



6 Strieker's "Histology," vol. i. Syd. Soc. Translation. 



