106 NERVOUS TISSUE. 



fibres without double contours) ; the sheath can be readily recog- 

 nised at individual points ; the grumous, but very finely granular 

 pulp appears to fill the whole cylinder, although by a proper mode 

 of arrangement the axis-cylinder may be traced with the greatest 

 distinctness within the nerve-fibre, following a straight rather than 

 a coiled direction. If the preparation has been very thoroughly 

 unravelled, the axis-cylinder may often be seen protruding from 

 T Vth to |th of a line beyond one of the uninjured nerve-fibres, 

 being generally straight or slightly bent, rounded, and of a faint 

 yellow colour; but occasionally presenting a somewhat coiled 

 appearance. 



The aqueous solution of iodine acts upon the nerve- cells in 

 nearly the same manner as upon the fibres. 



Milton's reagent (subnitrate of mercury with nitrous acid) ren- 

 ders portions of nerve hard and tough, and gives them an intense 

 purple colour. The individual bundles do not admit readily of 

 being separated into fibres. Under the microscope the nerve- 

 sheath exhibits a sharp outline ; the pulp is not so coarsely granu- 

 lar as after the application of chromic acid, nor so delicate as after 

 the action of hydriodic acid. The granules render the whole nerve- 

 tube very dark, and prevent the recognition of the axis-cylinder. 

 In preparations obtained by unravelling or teasing, we see, however, 

 a number of axis-cylinders either isolated or projecting in a very 

 twisted form from a portion of undestroyed nerve-fibre. The 

 microscope scarcely shows any trace of colour in the individual 

 nerve-fibres, or, at most exhibits only a yellowish, and not a violet 

 colour. 



A solution of corrosive sublimate, which is especially recom- 

 mended by Purkinje for the exhibition of the axis-cylinder, acts 

 independently of the coloration in very nearly the same manner 

 as subnitrate of mercury ; but the use of this reagent scarcely 

 facilitates the detection of the axis-cylinder within the uninjured 

 nerve-tube more than the preceding fluid. 



The grey cerebral substance, and the sympathetic ganglia 

 harden when immersed in solutions of these two metallic salts. 

 The nerve-cells slightly shrivel, and the cell-membrane is rather 

 more distinct : the contents become more grumous and un trans- 

 parent, so that the nuclei cannot easily be detected, and the nucleoli 

 only with great difficulty. 



A very concentrated solution of chloride of calcium renders 

 small nerve-bundles somewhat transparent, but at the same time 

 extremely tough and elastic, so that it is only with great care that 



