Obersteiner; The Structure of the Nervous System. 79 



protoplasmic processes anastomose with neighboring cells; i. e. 

 pass over directly into them. Appearances obtained by the 

 method of silver impregnation seem to speak with the greatest 

 distinctness against such connection. Tiiese terminal fibres may 

 interlace so as to make a dense felt, but a direct connection 

 seems to be excluded. Nevertheless, in the spinal cord of the 

 electrical fishes at the point where the nerves for the electrical 

 organs arise, Fritsch has observed very broad anastomoses be- 

 tween neighboring cells. 



II. The verve fibre. Several kinds of nerve fibres can be 

 distinguished ; but they all have one histological element, whose 

 presence is the sole characteristic of nerve fibres and which is 

 considered the only carrier of physiological energy — the axis- 

 cylinder. We shall, therefore, limit ourselves to the considera- 

 tion of the a.vis-cylinder and pass by the medullary sheath, 

 sheath of Schwan-n, etc., since the first alone concerns the ques- 

 tion of the inner relations of the nerve elements. 



Touching the finer structure of the axis-cylinder, we have 

 already seen, while speaking of the cell protoplasm, that the 

 fibrillar theory and the theory of the hyaloplasm stand m oppo- 

 sition to each other. I might now add that Heitzmann (Jour, 

 of Nerv. and Ment. Dis., 1890) regards the spongioplasm as 

 contractile protoplasm and seeks for the material expression of 

 nervous transmission in its varying contractions. 



Our knowledge of the axis cylinder has been materially 

 broadened by Golgi. Ramon yCajal, and KoUiker. These in- 

 investigators have shown that from the axis-cylinder of all lon- 

 gitudinal fibres of the spinal cord lateral twigs pass off almost 

 at a right angle. There can be followed a greater or less dis- 

 tance into the gray substance and here they break up into a 

 brush. It is, however, not improbable that all of the central 

 nerve fibres send out " collaterals" of this sort, so that an iso- 

 lated tract probably does not exist ■ within the central nervous 

 system . 



III. The terminal brush. We have said that every nerve 

 fibre, at the end opposite its origin from the cell, breaks up into 

 the, finest terminal branchlets, which are called the termirtal 

 brush. Such terminal brushes may radiate in the gray substance 

 of the central nervous system; they may, however, also lie at 



