THE NERVOUS TISSUES. 1005 



lost in the surrounding complex of glia-fibres. In young tissue the apical processes 

 often exhibit evidences of breaking up into a number of fine fibrillae. Where the 

 processes enter robust tracts of neuroglia, as in the posterior longitudinal septum of 

 the spinal cord, they are of unusual length. In addition to the radially directed 

 fibres connected with the ependymal cells, the fibre-complex of the ependymal zone 

 includes many fibrillae that are circularly and longitudinally disposed. Scattered 

 glia cells, some stellate but mostly small, are also present and represent the elements 

 from which the neuroglia-fibrillae have been derived. 



In the preceding account of the elements composing the nervous tissues the neurones have 

 been regarded as the morphological units, each retaining its individual anatomical indepen- 

 dence, although functionally closely related with other similar units. This conception, com- 

 monly referred to as the Neurone Doctrine and strikingly formulated by Waldeyer in 1891, 

 stands in contrast to the prior views by which actual continuity was attributed to the nerve-cells 

 by means of the union assumed to exist within the terminal net-works of their processes. The 

 independence and true relation of the neurone was established largely through the convincing 

 embryological investigations of His and the renewed study of the nerve-cells as demonstrated 

 by the improved applications of the Golgi silver-impregnations, supplemented by the method 

 of vital staining by methylene blue introduced by Ehrlich. The Neurone Doctrine has gained 

 wide acceptance and the support of the most distinguished anatomists, among those who have 

 materially strengthened its position being Kolliker, Ramdn y Cajal, Retzius, Lenhosse'k, 

 Waldeyer, van Gehuchten, and Edinger. 



The neurone conception, securely founded as it is upon a vast mass of evidence collected 

 from a wide field by the most painstaking and accurate observation, has not escaped challenge, 

 and at present is assailed by a group of histologists headed by Apathy and Bethe, who not only 

 bitterly oppose the integrity of the neurone as an independent unit, but also strive to depose the 

 nerve-cell from its dignity as the fundamental physiological factor. In 1897 Apathy 1 published 

 his observations on the structure of the ganglia of certain invertebrates, as revealed by a new 

 mercuric gold-chloride method, and thereby established the important fact that the cell-body 

 and processes of the neurone are pervaded by fine neurofibrillae, thus confirming the fibrillar 

 structure of the nerve-cell advanced by Max Schultze more than a quarter of a century before. 

 Following Apdthy, Bethe 2 investigated the tissues of the higher animals and succeeded in dem- 

 onstrating the existence of the neurofibrillae within the neurones of man. According to these 

 observers, the neurofibrillae, although interlaced without junction within the cell-bodies, are 

 independent threads, that are not confined to the neurones but pass beyond and unite with 

 fibres from other sources. The neurofibrillae, therefore, and not the nerve-cells, are the essen- 

 tial elements of the nervous system, the cells being only interposed along the path of conduc- 

 tion. Indeed, according to these views, the neurofibrillae are independent of and, in a sense, 

 foreign to the nerve-cells, leaving or entering the latter at pleasure and constituting by their 

 union a continuous path of conduction from the receptive element to the muscle-fibre. Apathy, 

 moreover, assumes the existence throughout the central nervous system of a fibrillar net-work 

 formed outside and between the nerve-cells by the neurofibrillae from which the axones may 

 arise independently of the nerve-cells. It is evident that if such be the case the conception of 

 the neurone as an individual unit falls. 



The criticism made by the newer school, that the supporters of the neurone theory relied 

 upon methods which inadequately demonstrated the ultimate terminal relations (the assumed 

 union in net-works) has been met by the introduction of the still newer methods of Beilschow- 

 sky and especially of Cajal, which have yielded preparations that demonstrate that the neuro- 

 fibrillae everywhere form net-works within the cell-bodies of the neurones, are confined to their 

 processes, and even in their ultimate endings form ununited terminal arborizations. It seems, 

 indeed, that, at present at least, the defenders of the neurone theory may with justice charge 

 their opponents in turn with depending upon methods that only partially show the relations of 

 the neurofibrillae within the neurones. Retzius, than whom no more experienced and competent 

 authority in this difficult field of research can be consulted, has recently reviewed the entire 

 question and presented 3 most convincingly the facts that enable him, as well as the most 

 distinguished anatomists of to-day, still vigorously to champion the Neurone Doctrine. After 

 a critical and scientific discussion of the arguments advanced by Apathy, Bethe and Nissl, 4 

 Retzius rests his case with little concern as to the verdict of those to whom facts and not 

 speculation most appeal. 



1 Mitteilungen aus d. Zoolog. Station zu Neapel, Bd. xii., 1897. 

 * Allgemeine Anat. u. Physiol. des Nervensystems, 1903. 

 3 Biologische Untersuchungen, N. F., Bd. xii., 1905. 

 4 Die Neuronenlehre und ihre Anhanger, 1903. 



