32 LISTER AND TURNER, ON THE 



substance of Schwann presented, in the larger fibres, the 

 same concentrically arranged appearance as we had ob- 

 served in the sciatic nerve, as is illustrated by figs. 6 and 7, 

 of which fig. 6 is one of the largest met with, being -gfo of 

 an inch in diameter, while fig. 7 is as small as ^Vgs of an 

 inch in transverse measurement. In the very minute fibres 

 no appearance of concentric lines could be detected, yet, 

 wherever the existence of an axial cylinder Avas indicated by 

 a carmine point, a ring of medullary sheath was always visi- 

 ble, presenting the same proportion to the axial cylinder as 

 in fibres of larger size. This may be gathered from figs. 8, 

 9, and 10, of which fig. 8 measures ^-J^o of an inch across, 

 fig- 9 W^ and fig. 10 only T% fo z . 



At the margins of longitudinal sections of the cord, the 

 contrast, both in structure and in tint, between the axial 

 cylinder and the medullary sheath showed itself very beauti- 

 fully. It often happened that a projecting isolated fibre 

 was, near its extremity, more or less divested of the white 

 substance of Schwann, so that the delicate, carmine-tinted 

 axial cylinder was exposed, though presenting here and there 

 colourless flakes of the medullary sheath adhering to its sur- 

 face; while in parts where the nerve was still entire, the 

 pink colour of the central fibre could be distinctly discerned 

 through the intervening white substance. Fig. 11 repre- 

 sents a large fibre under such circumstances, and fig. 12 one 

 of considerably smaller size ; and these sketches also display 

 the remarkable fibroid arrangement which we find the white 

 substance of Schwann invariably assumes under the influence 

 of chromic acid. 



In conclusion, we may remark that the successive employ- 

 ment of chromic acid and carmine seems likely to afford 

 valuable aid in discriminating nerve-fibres among other 

 structures ; there being, so far as we are aware, no other 

 form of tissue which, after the use of these means, exhibits 

 fibres having a central carmine axis, and peripheral un- 

 coloured sheath. 



Supplementary Observations by Mr. Lister. 



The fibroid arrangement of the white substance of Schwann 

 in nerves hardened by chromic acid has been minutely de- 

 scribed by Stilling, in his elaborate treatise on the 'Nerve- 

 fibre and Ncrvc-cell/* a work which we had not seen when 



* ' Ucbrr den Ban dcr Ncrven-Primitivfaser und der Ncrvenzelle.' Vou 

 Dr. B. Stilling. 1856. 



