30 



NERVOUS SYSTEM AND GENERAL SENSATION. 



having a mean diameter of from 1 -200th to 1 -300th of a line, 

 and always proceeding distinct from one another, never anas- 

 tomosing. These are the PRIMITIVE FIBRES of the nerve (figs. 



9, et seq.) If these 

 fibres have under- 

 gone little or no 

 change, each is se- 

 verallv seen to be 



* 



bounded by a dou- 

 ble contour an 

 appearance which 

 must be viewed as 

 the optical expres- 

 sion of a transpa- 



\\lilltltl fj/ '! rent covering or 



membrane. The 



middle space is 

 completely trans- 

 parent. When the 

 Fig. 9. A, Primary fibres of a human body, nerve has suffered 

 B, primary fibres (more highly magnified) of the change from pres- 

 ^ rain * sure, imbibition of 



water, or the like, the appearance is altered. In the middle clear 

 space granular or grumous particles or masses are perceived, 

 which, under pressure, escape from the divided ends of the' 

 primitive fibres (fig. 9, A, to the right). Other changes, but 

 more difficult of apprehension, also take place in the lateral 

 contours of the fibres, which are made up of the double lines. 

 To observe the primitive fibres of nerves in their normal 

 situation, the best subject is the delicate flat muscle of some 

 small animal one of the muscles of the eye of the common 

 sparrow, for example (fig. 10) which must be gently pressed 

 between two plates of glass. Here, in the middle trunk (a), 

 which, to the naked eye, looked finely fasciculated only, a 

 great number of primitive fibrils are perceived lying over one 

 another, but without running altogether parallel, inasmuch as 

 some diverge a little to the right, others a little to the left, 

 some proceed from below upwards, others from above down- 

 wards, but all preserve the main course onwards. They lie 

 BO close, and cover each other so much, that their structure 

 individually cannot be distinctly made out. At the parts 



