MULLENIX: EIGHTH CRANIAL NERVE. 243 



The intracellular rings and the protoplasmic bridges connecting 

 them with the axis cylinders which Bielschowskv und Briihl have 

 described are unique, having been recorded by no other investigators. 

 The observation is interesting, in that it affords a suggestion of histo- 

 logical evidence in support of the theory of the synapse between 

 neurones, which has been advocated by Sherrington (:06). It has been 

 found that nerve conduction in which two or more neurones are in- 

 volved is much slower than conduction along an axis cylinder of a 

 single neurone. Mislawsky ('95) found that the direction of the 

 nervous impulse is reversible in nerve-trunk conduction, whereas in 

 reflex-arc conduction it is irreversible. These and other physiological 

 differences between nerve-trunk conduction and reflex-arc conduction 

 Sherrington has referred to that part of the arc which lies in the central 

 gray, and he has introduced the term synapse to represent those "in- 

 tercellular barriers" in the central gray which constitute the nexus 

 between neurone and neurone. If the view that the sense cells are 

 nervous in character should prove correct, the protoplasmic bridges 

 which Bielschowsky und Briihl have described in the periphery might 

 be regarded as representing the synapse for which Sherrington adduces 

 so much physiological evidence in the spinal cord. The neurones 

 involved in audition are so short and other conditions are such as to 

 render it impracticable to obtain, in this structure, physiological 

 evidence of the kind that Sherrington has obtained by experimentation 

 upon spinal nerves. But the confirmation of the existence of the 

 protoplasmic bridge would be interesting because it would supplement 

 the physiological evidence obtained from other regions. 



I must say, however, that I do not believe that the existence of 

 either the intracellular rings or the protoplasmic bridges can be re- 

 garded as established until confirmed by other investigators. My 

 preparations furnish no evidence of the existence of the protoplasmic 

 bridges, and only slight evidence of intracellular nervous material. 



In conclusion, it may be stated that in so far as Bielschowsky 

 preparations may be relied upon as revealing the actual conditions, 

 we are justified, in the case of the fishes, in regarding the relation 

 between nerve terminals and sense cells as one of contact, and not of 

 organic union, and the relation between different axis cylinders as, 

 likewise, one of contact rather than continuity. Such preparations 

 make it possible to trace nerve courses more completely than do Golgi 

 preparations, and there is the additional advantage that neurofibrillae 

 are differentiated, as they are by methylene blue. ]My results bear 

 out the conclusions of those investigators who have studied the problem 



