THE NERVOUS SYSTEM. 



409 



Fig. 158. 



are torn into fibres as carefully as possible under a simple microscope, 

 until the fibres are traced to their origin, which may be done with a 

 little trouble in almost every ganglion, or the small ganglia of the fifth 

 sacral and coccygeal nerves are taken for the purpose. In these gan- 

 glia, in almost every individual, solitary and completely isolated, pedun- 

 culated, ganglion-globules are met with, close to or in the neighborhood 

 of the ganglia, each in its special sheath, which in this case appears to 

 be homogeneous (Fig. 157), and in many cases, the simple, dark nerve- 

 fibres lying in the peduncle of the globule, and frequently also its con- 

 nection with the cell, by means of a pale process, may be distinctly 

 perceived. In the ganglia aberrantia also of Hyrtl, that is to say the 

 inconstant, larger or smaller collections of nerve-cells, which are found 

 in every subject upon the posterior roots of the 

 larger nerves, the simple origins of fibres may 

 occasionally be distinctly noticed. The dark- 

 colored fibres, arising from the nerve-cells, 

 simply constitute the continuation of the pale 

 processes of the cells, so that the membranes 

 and contents of each part pass continuously 

 into each other, and thus also the membrane 

 and the contents of the cells are connected with 

 the sheath of the nerve-tubes, the medullary 

 sheath, and the axis-cylinder. In older nerve- 

 cells, or by the operation of reagents (ar- 

 senious acid, chromic acid, iodine), the con- 

 tents of the cell become detached from the 

 membrane, and the axis-cylinder appears 

 as a direct continuation of the former (Fig. 

 158), as was first shown by Harting (vid. 

 also Stannius in " Gbtt. Anzeig.," 1850, 

 and Ley dig, 1. c. Tab. 1, Fig. 9), which 

 is the best proof that the contents of the 

 nerve-cells cannot be understood as contained in a dilated nerve-tube.* 



FiQ. 158. Nerve-cell of the Pike (bipolar, as they are termed), which is continued at each 

 end into dark-bordered nerve-tubes, treated with arsenious acid : a, sheath of the nerve-cell ; 

 6, sheath of nerve ; c, nerve-medulla ; d, axis-cylinder continuous with the contents of the 

 nerve-cell ; e, which have shrunk away from the sheath. Magnified 350 diameters. 



* [The axis-cylinder is supposed by some observers not to be, as above stated, a continua- 

 tion of the contents of the cell, but rather of its nucleus. This continuation of the nucleus 

 into the.axis-cylinder is best seen in ganglia, which have been kept for some days in diluted 

 acetic acid. We are thus, according to Axmann (1. c.) not only able to see the connection of 

 the axis-cylinder with the nucleus, but also to isolate the nucleus with a portion of the axis- 

 cylinder attached to it. This continuation of the nucleus of the ganglion cell into the axis- 

 cylinder has been observed in all classes of animals. It was first described by Harless in 

 the ganglion corpuscles of the electric lobes of the Torpedo Galvani. DaC.] 



