THE NERVOUS TISSUE. 51 



in size in different situations. The nerve-fibres usually pass amongst 

 them, Fig. 29, d ; and, whilst some of the branched oifsets of the cells 



Fig. 27. (Kolliker and Hannover.) Colored cells, containing nuclei, called nerve-cells, ganglionic cells, 

 or ganglionic corpuscles, a, culls of simple form from a sympathetic ganglion, b, branched cells, or stel- 

 late cells, from the gray substance of the spinal cord, c, branched cells of larger size from the medulla 

 oblongata. d, simple and branched cells from the superficial part or convolutions of the brain, e, a large 

 cell from the gray substance of the cerebellum. Magnified about 100 diameters. 



serve undoubtedly to connect different cells together, others, it is 

 stated, are continuous with the tubes of the white or tubular nerve- 

 fibres. It is important to note, however, that this latter statement, 

 though probably correct, is more a matter of inference than of direct 

 observation, in so far at least as concerns the brain and spinal cord of 

 man and the higher animals. In the ganglia, however, both in man 

 and animals, this connection has been distinctly seen. According to 

 the number of their 'offsets and connections, nerve-cells have been 

 named unipolar, bipolar, or multipolar. Cells apparently destitute of 

 them are described as apolar. The existence of such free cells has 

 however been denied ; and the so-called unipolar cells are said to have 

 another filament passing from them, often twisted round the one which 

 is more evident (Beale). 



The gray or gelatinous fibres (Remak's fibres) are very simple in 

 structure, being soft granular flattish fibres, having no distinct tubu- 

 lar and medullary investment, and containing many dark nuclei, Fig. 

 29, d. These fibres are most abundant in the sympathetic nerve and 

 its branches, but a few extend into the spinal and cranial nerves. 

 Some of these are regarded as connective tissue fibres, and not as 

 nerve-fibres at all. 



The white or tubular nerve-fibres, Fig. 28, b, are microscopic tubuli, 

 which when freshly examined in a perfect state appear to be homo- 

 geneous, but which, even on cooling, soon acquire a characteristic dark, 

 smooth, double outline or contour, 1, and which may quickly, from 

 pressure or other causes, become varicose or beaded, 2. Each tube 

 consists of an outer structureless membrane, inclosing a layer of trans- 

 parent fluid fat, or medullary matter, which, after death, 3, is apt to 

 lose its clear homogeneous appearance, and become congealed into 

 drops or masses, or to project from the broken or cut ends of the 

 tubes. Within this medullary matter, or ivhite substance of Schwann, 

 as shown in Fig. 28, 4, is a firmer part or core, called the central band- 

 axis, or axis cylinder, which is not fatty but albuminoid. This cen- 



