6 Mason — Central Nei'vous System of Rejptiles^ etc. 



tureless state of the axis cylinder, against the views of those 

 who believe in their fibrillary composition, enquires : "How 

 is it now with the connection between nerve-cells and nerve- 

 fibres? * * * * From my observations on fresh as well 

 as on hardened ganglia of the spinal nerves in fishes, amphi- 

 bia, warm-blooded animals and man, the union is of this 

 nature: the axis cylinder of the nerve fibre is the direct con- 

 tinuation of the cell substance;" and two pages further on, 

 "It seems to me impossible to see such a connection in sec- 

 tions of the brain and spinal cord ; it can only be done with 

 the help of isolating methods, as we are taught by the latest 

 observations of Koschewnikoff."* It will be observed that 

 although Stieda has not seen such a connection in a section, 

 he nevertheless considers it as a fact, wdiile Keissner, in 1864, 

 claimed to have seen it; and it was figured by ]*]cker and 

 Kiipfer. Dean f has also a plate showing, in the rabbit, a 

 nerve process joining a nerve-fibre of an anterior root, and 

 passing out as far as the peripherj'. The frequency with 

 which I have obtained sections from the brachial enlargement 

 of the froo;, which show in the clearest manner what becomes 

 of by far the greater part of the inferior root fibres of this 

 region, leads me to give here my manner of procedure. 



In the first place, I must assert, contrary to the opinion of 

 Keissner given above, that I know of no other animal so well 

 suited, and for so many reasons, as is the frog, for the study 

 of this point. It is true that the root-fibres in each section are 

 comparatively few; but this seems to mc an advantage rather 

 than an impediment, and if more nerve-fibres are desired, it 

 is quite easy to obtain them by making more sections. The 

 supplj" of froffs is ample ; and their spinal cords almost come 

 out of the spinal canal of themselves, so easy is their removal, 

 when the operation is done upon the abdominal side. As the 

 chief cause of failure lies in the division by the razor of the 

 nerve-tube somewhere between the cell and the periphery of 

 the cord, it follows that, coeteris paribus, the smaller the 

 diameter of the cord, the greater the chance of success. In 



* Archiv fur Microsk. Anat. Bd. V. 18G9. 



f J. Dean. — Microscopic Anatomy of the Lumbar Enlargement of the Spina] 

 Cord. 1861. 



