I5O THE TISSUES. 



case of large cells there is a similar area around the nucleus, the 

 inner border of which belongs to the nuclear membrane. H. Held 

 has found that the chromatophile granules are brought out by treat- 

 ment with alcohol and acid fixing fluids, but not in alkaline or neu- 

 tral. They appear, according to the treatment, as fine or coarse 

 granules. They can not be seen in fresh nerve-cells. He conse- 

 quently regards them as artefacts precipitations of the protoplasm 

 due to reagents (vid. A. Fischer). At its junction with the cell the 

 neuraxis spreads out into a cone which is entirely free from granules, 

 and apparently fitted into a depression in the granular substance of 

 the cell (implantation cone or axone hillock). The shape, number, 

 and size of the tigroid granules vary with the physiologic activity of 

 neurones. They practically disappear from the neurones in certain 

 diseased conditions or after the administration of poisons which affect 

 more particularly nerve-cells ; also after extreme fatigue. 



The cellular substance between the chromatophile granules con- 

 sists also of very fine, highly refractive granules, which appear to be 

 arranged in a reticulum surrounding the chromatophile granules 



Nucleus. ^^r. 



Nucleolus. 

 Fibrillar structure. 

 Medullary sheath. 



Fig. 107. Bipolar ganglion cell from the ganglion acusticum of a teleost (longitu- 

 dinal section). The medullary sheath of the neuraxis and dendrite is continued over the 

 ganglion cell ; X 800. 



(vid. Nissl, 94, and v. Lenhossek, 95), and the recent observations 

 of Apathy and Bethe make it very probable that in the intergranular 

 substance of the protoplasm of the nerve-cell there exist very fine 

 fibrils which may be traced into the processes of the cell, and from 

 the branches of one neurone to and into the branches of other neu- 

 rones without interruption. It requires, however, further observation 

 before more positive statements may be made concerning them. 



Besides the granules above mentioned, and which are revealed 

 by special methods, there are found in the protoplasm of many of 

 the larger nerve-cells pigment granules of a yellow or brown color 

 which stain black with osmic acid. 



The dendrites are usually relatively thick at their origin, but 

 gradually, as a result of repeated divisions, taper until their widely 

 distributed arborescent endings appear as minute threads of widely 

 different shapes. When treated by certain methods, they present 

 uneven surfaces studded with varicosities and nodules, in contradis- 

 tinction to the neuraxes, which are smooth and straight. Their ter- 

 minal branches end either in points or in small terminal thickenings. 

 The groups of terminal end-branches of a dendrite (also of a neur- 

 axis) are known as telodendria (Rauber), or end-branches. The 



