254 



THE CAT. 



[CHAP. ix. 



22*93 ; phosphate of iron, 1-23 ; phosphate of lime, 1/62 ; phosphate 

 of magnesia, 3'4 ; chloride of sodium, 4-74 ; sulphate of potash, 

 1*64 ; free phosphoric acid, 9'15 ; and silicic acid, 0'41. 



The STRUCTURAL ELEMENTS of nervous tissue are mainly of two 

 kinds : (1) fibres, and (2) nerve- cells or corpuscles. The former of 

 these elements makes up the hulk of the peripheral part of the 

 nervous system, while the corpuscles abound in its axial portion and 

 in its scattered ganglia. 



The NERVE FIBRES are again divisible into two kinds : (1) the 

 white or tubular nerve fibres, and (2) the grey or pale fibres. 



The white fibres, which form the bulk of all the nerves except 

 those of the sympathetic system, are nearly cylindrical filaments 



2, 3 2 



Fig. 121. WHITE NERVE FIBRES. 



A. White or meclullated nerve-fibres, showing 



their sinuous outline and double contours. 



B. Diagram showing the parts of a medullated 



fibre, viz. : 



11. Primitive sheath. 



2 2. The white substance, or medullary 

 sheath. 



3. The axis-fibre, or axis-cylinder some- 

 times called the primitive band. 



C. Diagram intended to represent appearances 



occasionally seen in the tubular fibres, viz. 

 1 1. Membrane of the tube, seen at part 

 where the white substance has separated 

 from it. 



2. A part where the white substance is 

 interrupted. 



3. Axis projecting beyond the broken end 

 of the tube. 



4. Tarts of the contents of the tube which 

 have escaped. 



which, during life, seem composed of a clear, oily, semi-fluid sub- 

 stance, but after death, appear as composed of a delicate structureless 

 outer membrane the primitive sheath (like the sarcolemma of muscle 

 fibre), provided with large nuclei, and containing fatty fluid termed 

 the medullary sheath or white substance of Schwann, through which 

 runs a thin central thread of albuminoid matter called the axis cylinder. 

 The largest of these white nerve-fibres has a diameter of about 

 tne TaW f an i ncn > but some f on ly TTTO-O--O-- They may be larger 



