42 



NERVE FIBERS. 



72. Myelinic (meduUated) nerve fibers. Cat. Isolated 

 fibers from the sciatic nerve. Hardened in Miillers fluid 8-10 

 days ; hardened in alcohols ; dehydrated ; in chloroform 1-2 days ; 

 95% alcohol ; 82% alcohol ; water ; stained in Delafield's hematoxy- 

 lin 12-24 hours (§ 82) ; now in clearer. With needles tease out a 

 small bundle of fibers, keeping them parallel if possible. Mount in 

 balsam. 



In studying this preparation, determine the axis cylinder, the 

 myelinic sheath, the nodes of Ranvier, the internodes, — their 

 length, — the nerve corpuscles (nuclei). Can you recognize the 

 neurilemma ? Does the preparation show medullary segments or a 

 reticular structure of the myelinic sheath ? 



73. Amyelinic nerve fibers. Ox. Isolated fibers from the 

 splenic nerve. Assigned for study. Dissociated in -^X osmic acid 

 (§ 17) ; teased apart with needles. 



Both myelinic and amyelinic fibers are present, and care must 

 be exercised in distinguishing between delicate myelinic fibers and 

 the amyelinic ones. When a good place is found, study the amye- 

 linic fibers, noting, as compared with the myelinic nerve-fiber, the 

 absence of the myelinic sheath and the greater number of nerve 

 nuclei. Compare the myelinic fibers in this preparation with those 

 in 72. The myelin of the sheath is retained and blackened in 73 ; 

 in 72 it has been dissolved out, 



PERIPHERAI, NERVES. 



74. Sciatic nerve. Cat. Transection ; chrome-oxalic 

 (§ 32) ; paraflBn ; sections fi. Stain with hematoxylin 15 

 minutes, picrofuchsin ^ minute. Mount in balsam. 



Study this preparation for (a) the structure of a nerve trunk, 

 noting its component funiculi or bundles, surrounded by connective 

 tissue sheaths, the perineurium, and bound together by the epi- 

 neurium, while within the funiculi, the individual nerve fibers with 

 the endoneurium ; {b) the structure of myelinic nerve fibers in tran- 

 section, showing the central axis-cylinder, surrounded by the mye- 

 linic sheath (the myelin dissolved out). Find a place where a 

 nerve nucleus is cut. Compare with the transection of a muscle, 

 recognizing the analogy in the relations of the connective tissue. 



