THE MICROSCOPE IN ANIMAL HISTOLOGY. 199 



hollow tubes, conveying fine ethereal fluids, termed ani- 

 mal spirits. 



Nervous matter is soft, unctuous, and easily disturbed, 

 hence it is necessary to examine it while fresh. Histo- 

 logically it is divided into fibres and cells, imbedded in 

 connective tissue. 



Nerve-fibres are of two kinds, tbe medullated, or dark- 

 bordered threads, and the pale, or non-medullated. Med- 

 ullated fibres consist of a delicate envelope of connective 

 tissue, called the neurilemma or primitive sheath, an axis- 

 cylinder or albuminous portion, extending down the cen- 

 tre, and a portion composed of a mixture of albumen, 

 cerebral matter, and fat, surrounding the axis-cylinder 

 (Plate XXI, Fig. 155, A, B, c). This latter is the medul- 

 lary sheath, or white substance of Schwann. It changes 

 rapidly, so as to coagulate and become granular. Alka- 

 lies render it fluid, so as to exude in fat-like drops. Ab- 

 solute alcohol, chromate of potass and collodion, contract 

 the sheath, so as to permit the axis-cylinder, which is the 

 essential part of the nerve, to protrude (Plate XXI, E, 

 Fig. 155). Anilin, carmine, nitrate of silver, and chloride 

 of gold stain the axis-, while osmic acid blackens only the 

 medullary sheath. 



Non-medullary or pale nerve-fibres are regarded as em- 

 bryonic or developmental forms (Plate XXI, D, Fig. 155). 

 The ganglionic fibres of the sympathetic (Remak's fibres) 

 are flat, homogeneous bands, with round or oval nuclei. 

 Some have considered them as formed of connective tis- 

 sue, but their nervous character is generally conceded. 



Schultze and others regard the axis-cylinder as made up 

 of extremely delicate fibrillse. 



Nerve-cells, or ganglion corpuscles, are of two kinds, 

 those without and those with processes. The first are 

 called apolar, and the latter unipolar, bipolar, or multi- 

 polar, according to the number of ramifications. The 

 cells are nucleated, and inside the nucleus is usually 



