522 



By examination with high powers (700 diameters), many fibres which 

 appear to be single when seen by lower powers can be resolved into 

 three or more, all enclosed in the same transparent tissue. As the 

 nerve- fibres approach their distribution, this transparent structure 

 becomes much spread out. It is intimately connected with nerve- 

 fibres and capillaries, and with them forms a delicate expansion over 

 the muscular fibres and in other parts ; delicate fibres also, in con- 

 nexion with the nerves and capillaries, may be observed in it. In 

 some cases this expansion seems to be incorporated with the sarco- 

 lemma, and it is probable that in certain instances it is really the 

 structure which has received that name. 



Axis cylinder and white substance. The author has been led to 

 conclude that, in consequence of the free division of the axis cylinder 

 and white substance near the point of distribution of the nerve, a 

 single fibre in the trunk of a nerve may carry impressions to or from 

 a much larger extent of surface than is generally supposed. The 

 white substance which surrounds the axis cylinder gradually dimi- 

 nishes, until, in the finer ramifications, it is impossible to say that a 

 fibre consists of an axis cylinder and white substance ; for its general 

 appearance and refractive power are the same in every part, except 

 where the nuclei are situated. The author considers that the defi- 

 nite characters of the axis cylinder and white substance in the trunks 

 of the nerve, may be due to the gradual growth and altered relations 

 of the fibres which occur during the development of the entire or- 

 ganism. In the ultimate ramifications the whole fibre seems to con- 

 sist of a very transparent and perhaps delicately granular substance, 

 but no tubular membrane, medullary sheath, or axis cylinder can be 

 demonstrated as distinct structures. 



Of the formation of new fibres. In connexion with the terminal 

 ramifications, new fibres are being continually developed by the 

 division of the nuclei, and old ones undergo removal. The remains 

 of the latter may, however, be seen in the form of very delicate fibres, 

 in connexion with active nerve-fibres. The author regards much of 

 the so-called connective tissue between the elementary fibres of 

 muscle and in some other situations, as of this nature, as the remains 

 of structures whose period of functional activity was past, and 

 which have been removed, all but this small quantity of insoluble 

 material. 



