98 NERVOUS TISSUE. 



forming bundles of a somewhat bluish grey colour, whilst the 

 cerebro- spinal fibres appear white and of a silvery lustre. They 

 are, however, found interspersed in various quantities in all other 

 nerves, more especially in those of the involuntary muscles, the 

 skin, and the mucous membranes (Bidder and Volkmann*), and 

 lastly in the posterior roots of the spinal nerves and in those of 

 the sensitive cranial nerves (Kb'lliker)t. It is only in the peri- 

 pheral extremities of the cerebro- spinal nerves that the animal 

 fibres become so attenuated that they resemble in their diameter 

 and general appearance the above-described sympathetic fibres. 

 These nerve-fibres are also inclosed in a sheath, which cannot 

 always be distinctly recognised, even after the application of 

 chemical reagents ; on the other hand, the axis-cylinder may be 

 very easily brought into view in these nerves by chemical means, 

 which we shall notice more particularly in a future page. 



Nerve-fibres containing no medulla have been detected by 

 R. Wagner, Remak, Bowman, Kolliker, and other histologists, in 

 the pale fibres of the Pacinian corpuscles, in the extremities of the 

 olfactory nerves, in the nerves of the cornea, in the electrical 

 organ of the Torpedo and Ray (where there is an actual ramifica- 

 tion of the fibres), and in the extremities of the nerves of the skin 

 of the mouse. These fibres appear from the observations hitherto 

 made in relation to this subject, to consist only of a sheath and an 

 axis-cylinder. 



Another class of nervous fibres has been assumed to exist, 

 namely, Remak's fibres, in which nuclei may be detected, more 

 especially after the addition of acetic acid; but it has not yet been 

 decided whether these elements -which have been observed in the 

 ganglia of the sympathetic, &c., are true nerve-fibres, or merely a 

 peculiar form of connective tissue. 



Larger or smaller bundles of nerve-fibres are surrounded by a 

 fibrous, strongly glistening, white, dense membrane, called the 

 neurolemma. It appears on a closer examination to consist of 

 different forms of connective tissue, with which are interspersed 

 numerous elastic fibres. 



The Pacinian bodies form a very singular appendage to the 

 nerve-fibres. These bodies, which are present in very large numbers 

 in the hands and feet of man and many carnivorous animals, and 

 in the mesentery of the cat, are oval, consist (somewhat like onions) 



* Die Selbststandigkeit des sympathischen Nervensystems. Leipzig, 1842. 

 + Selbststandigkeit und Abhangigkeit des sympathischen Nervensystems. 

 Zurich, 1844. 



