TURNER, ON NERVE-FIBRES. 151 



have succeeded in obtaining extremely satisfactory views of 

 the axial cylinder, and of the proportion which it bears to 

 the medullary sheath. From the great simplicity and pre- 

 cision of this process, I am induced to make the following 

 communication. 



Portions of an ordinary spinal nerve, previously hardened 

 by immersion in chromic acid, were placed for a few hours in 

 an ammoniacal solution of carmine. After being removed 

 from this solution, they were washed with water, spread 

 out on a glass plate, and then treated with spirit, turpentine, 

 and Canada balsam in the ordinary way. They were then 

 examined under a good one-fifth inch object-glass in their 

 entire state, without sections being made through them, 

 either in one direction or another, the fibres lying in their 

 natural position parallel to each other. 



In the various fibres of the bundle, the axial cylinder was 

 seen to be deeply tinted by the carmine. It could be traced 

 along the centre of the fibre, occupying its middle third, and 

 presenting a perfectly clean and sharply defined outline. 



In none of my preparations have I been able to see any of 

 those " ramifications " of the axial cylinder into the medul- 

 lary sheath, which have been so elaborately figured and 

 described by Stilling. 



A careful examination of the numerous figures given by 

 him in the twenty-fourth plate of his great work, and a com- 

 parison of these figures with my own preparations, convince 

 me that the structures which he has described under that 

 name are nothing more than small fibroid particles of the 

 medullary sheath itself, and quite distinct structurally from 

 the axial cylinder. If they had been actual prolongations of 

 the axial cylinder, they would, like it, have received the car- 

 mine colour, which, so far as I have seen, never takes 

 place. 



I cannot agree, either, with the opinion expressed by Stil- 

 ling of the coDnection of the different fibres in a bundle by 

 means of fine elementary tubules passing between them. 

 Each fibre in my preparations possessed a distinct and well- 

 marked unbroken outline, the only intermediate material 

 that I have seen being an extremely delicate, wavy con- 

 nective tissue, which, although lying between the fibres, does 

 not in any sense form a part of them. Nerve-fibres, examined 

 in this manner in their entire condition, afford to the ob- 

 server, in a more satisfactory way than is permitted by any 

 other process with which I am acquainted, a means of arriv- 

 ing at precise conclusions respecting the absolute differences 

 between the axial cylinder and the medullary sheath. In 

 them the almost perfectly homogeneous axis contrasts strongly 



