xl Journal of Comparative Neurology. 



The sections, cut after paraffin embedding, were mordanted for five hours 

 in warm copper acetate two-thirds saturated, and stained in Kultschitzky's hse- 

 matoxylin for 12 hours. They did not take up the stain properly. 



69 M. Another specimen was prepared exactly like the last save that the 

 alkaline hematoxylin (Weigert's) instead of the acid stain of Kultschitzky's was 

 used. The sections take up the stain well and when decolorized by the method 

 of VVeigert give excellent differentiation. 



These sections have a very different appearance from any of the Flemming 

 hardened specimens. The fibers under the high power exhibit the more usual 

 appearance of ordinary Weigert sections, i. e., the fibers, both large and small, 

 are stained a deep blue black, the entire myelinic sheath and the axis cylinder 

 being uniformly colored. Upon further decolorizing the axis cylinder is left 

 deeply stained after the myelin has been almost completely cleared. This is, 

 then, an axis cylinder stain, as well as a myelin stain ; the naked collaterals and 

 terminal arborizations seem to take up and retain the dye and the " Punktsub- 

 stanz " is aUvays tinged with blue. All nuclei also retain the color. This, then, 

 is a very useful stain for fishes, as well as for reptiles. 



Summary. — Brains hardened in strong formalin have the nerves 

 well fixed, though not so faithfully as osmium hardened specimens. 

 It is an interesting fact that those methods which in Bolton's hands gave 

 the best results upon the human brain fail utterly when applied to fish 

 brains. This is doubtless due to chemical difference in the tissues, for 

 it is well known to all who have worked with the more delicate stain- 

 ing methods that even closely related animals often require different 

 treatment. It is, however, possible to get excellent Weigert prepara- 

 tions of fish brains that have been fixed in formalin by using the meth- 

 od of Edinger (No. 69). 



Vin. — FIXATION IN VARIOUS SALTS. 



As previously mentioned, the bichromate of potash, which is com- 

 monly used as a fixer for Weigert sections, does not preserve the nerve 

 sheaths with sufficient fidelity for my purposes. Strong formalin is, 

 however, a good preservative of nerve sheaths and it was tried in com- 

 bination with several salts which are known to act favorably as mordants. 



72 M. A young specimen was fixed for 5 days in a mixture composed of 

 iron alum 4 per cent, and formalin 10 per cent. Without further mordanting 

 the sections were .stained in one-half per cent, aqueous hematoxylin for three- 

 quarters of an hour and decolorized by the method of Weigert. The result was 

 no differentiation whatever. 



73 M. Other similar sections stained in Weigert's hematoxylin for 15 hours 

 and decolorized in 2 per cent, iron alum gave even worse results. 



74 M. Still other sections stained in acid hematoxylin and decolorized in 

 4 per cent, iron alum differentiated the nerve fibers quite well, though not so 

 well as the following. 



