332 Sheath Cells and A\-ono Slioat+is in the fVntrnl Xervons System 



oil composed of vqw.xl parts of carbolic acid crystals, xylol and oil of 

 ber<iamot. Xylol alone will clear the material, but it acts more slowly 

 and dries too quickly on the slide where it is necessary to spread out the 

 material before mounting. 



To mount, the greater part of the clearing oil was removed from the 

 material settled on the bottom of the dish, and then with the points of 

 fine forceps or with a teasing needle, a sufficient mass of the dissociated 

 fibers were lifted out and placed upon the slide and the surplus oil then 

 drained off or taken up by holding a bit of blotting paper near the mass. 

 A drop of balsam was then added and the fibers gently spread through it. 

 The cover glass placed squarely down upon the mount tends to further 

 spread the fibers out. Thus a preparation is obtained which is per- 

 manent and upon which the oil immersion may be used with convenience. 



Examination of the preparations shows that teasing with the stream 

 of water results in three advantages not obtained by teasing spinal cord 

 bv the ordinary methods: (1) Bits of nerve fiber are obtained of con- 

 siderably greater length than could be obtained with needles an,d the 

 fibers are nearly all isolated instead of in compact, broken clumps as 

 often results from needles. (2) The preparation is cleaner. The fibers 

 are washed out, leaving most of the plexuses of blood-vessels and the 

 coarser masses of connective tissue behind in the shred remaining pinned 

 to the wooden board. (3) The fibers themselves are clean. The neu- , 

 roglia fibers and nuclei and the general protoplasmic syncytium other- 

 wise surrounding and adhering to the fibers is washed off, especially from 

 those having acquired a medullary sheath. This adds greatly to the value 

 of the method for the purpose herein, in that almost every nucleus to he 

 seen is adhering closely to a nerve fiber and usually can be considered 

 to represent one of the sheath cells in question. 



Of the stains employed upon the sections, the Benda method proved 

 best for the seal-ring cells. The toluidin blue of this method seems to 

 especially differentiate these cells, staining their granular cytoplasm a 

 deeper blue than the general syncytial protoplasm and rendering the cells 

 more easily found than is the case after the more ordinary staining 

 methods. Most of the syncytium is stained light brownish-red by the 

 alizarin of the method, thus giving a background of good contrast. The 

 nuclei and the adult neuroglia fibers when present are, of course, stained 

 a dee|) blue. 



In all the figures the camera lucida was used in outlining the drawings 

 and the magnification in each was that obtained with ocular 4 and objec- 

 tive T2 (oil immersion, Zeiss). 



