MULLENIX: EIGHTH CRANIAL NERVE. 241 



structures described by Prentiss, Bethe, and others, are in reality 

 nervous in character. It is not uncommon to find adherents of the 

 neurone theory maintaining that the fibrillists have been misled by 

 over-impregnation, and it is no less common to find adlierents of the 

 fibrillar theory attributing the conclusions of neuronists to the incom- 

 plete impregnation of their material. 



It may well be recognized that the characteristics of nervous material 

 by which it may be differentiated from non-nervous material, in the 

 study of neuro-histological problems, are not so numerous nor so 

 varied as might be desired. A good deal of what we believe concern- 

 ing the physiology of the sense cells and nerve fibres, particularly in 

 the ear, rests upon analogical evidence which has not as yet been 

 confirmed by experiment. It is probably safe to assume, however, 

 that both the sense cells and the axis cylinders possess the physiological 

 properties of nerve tissue, which Gotch, in his article in Schaffer's 

 Physiology (:00), has characterized as "that tissue which exliibits 

 phenomena of excitability, conductivity, and states of excitation." 

 Without doubt these characteristics are possessed in common by sense 

 cells and nerve fibres, though probably in varying degrees. Since it is 

 as yet impossible to obtain direct evidence as to the functional differ- 

 entiation between them, we are forced to content ourselves with such 

 morphological evidence as is afforded by differential staining, and to 

 assume that those portions which exhibit peculiar affinity for silver 

 compounds are nervous in character, as is undoubtedly the case in 

 other places in the animal body, and that those which do not exhibit 

 such aflSnity are non-nervous. Such a distinction is of course entirely 

 inadequate as a general definition of nerv'ous material, but it constitutes 

 the best evidence that is obtainable at present, and it has seemed to 

 me that it is well to recognize the narrowness of the tests upon which 

 we are forced to rely in attempting to solve problems of this kind. 



My conclusion, then, regarding pericellular networks, is that the 

 nervous character of such networks is doubtful, but that no violence 

 would be done to the neurone theory by their confirmation. 



The theoretical significance of intracellular networks of neurofi- 

 brillae, such as Kolmer has described, and of such intracellular struc- 

 tures as Bielschowsky und Briilil have described, would depend to a 

 large degree upon their embryological origin and the relations of the 

 neurofibrillae of the sense cells to those of the axis cylinders. If it 

 should be shown that the sense cells of the auditory epithelium are not 

 secondary, but primary, sense cells, as is the case in the olfactory epi- 

 thelium, it would seem that Apathy is right in ignoring the cell bodies 



