382 CHAPTER XXXI. 



methods 011 brains of fifty rats, concludes that the best is Ohlmacher's. 

 The brain should be put into it for two to three hours, then for one into 

 alcohol of 85 per cent., then 70 per cent, with iodine for at least twenty- 

 four hours, then passed through ether into 2 per cent, celloidin for two 

 to three days, and passed through chloroform and benzol into paraffin. 

 Bourn's is the best of the formol liquids ; Tellyesnicky's is the only one 

 of the bichromate mixtures that equals it. All sublimate mixtures fix 

 nuclei well, but vacuolise cytoplasm. 



The reader will note that these results do not allow for subsequent 

 impregnation operations. 



744. Nervous Centres of Reptiles, Fishes, and Amphibia. 

 MASON (Central Nervous System of Certain Reptiles, etc. ; WHITMAN'S 

 Methods, p. 196) recommends iodised alcohol, six to twelve hours ; then 

 3 per cent, bichromate, changed once a fortnight until the hardening is 

 sufficient (six to ten weeks). 



BURCKHARDT (Das Centralnerveusystcni von Protopterus, Berlin, 

 1892 ; Zeit. wiss. Mik., ix, 1893, p. 347) recommends a liquid composed 

 of 300 parts of 1 per cent, chromic acid, 10 parts of 2 per cent, osmic 

 acid, and 10 parts of concentrated nitric acid, in which brains of Pro- 

 topterus are hardened in twenty-four to forty-eight hours. 



FISH (Journ. ofMorpkol., x. 1, 1895, p. 234) employed for Desmoijnathus 

 a mixture of 100 c.c. of 50 per cent, alcohol, 5 c.c. of glacial acetic acid, 

 5 grins, of corrosive sublimate, and 1 grm. of picric acid, fixing for 

 twelve to twenty-four hours, and passing through the usual alcohols. 



STHONG (Journ. coinp. Neurol., xiii, 1903, p. 296) fixes (and decalcifies 

 at the same time) the heads of young Acarithias in a mixture of 9 parts 

 of 5 per cent, iron alum and 1 part of forniol, for about two weeks, makes 

 paraffin sections, stains with hiematoxylin, and differentiates in iron alum 

 of 1 to 2 per cent. 



SECTIONS. 



745. IMBEDDING is by no means always necessary. Sections 

 can be obtained from any part of the central nervous system 

 without it. The material should be well hardened, and 

 glued 011 to a piece of wood or cork by means of a rather 

 thick solution of gum arabic. As soon as it begins to stick 

 to the support the whole is thrown into 80 per cent, alcohol 

 to harden the joint, after which it may be fixed in the object- 

 holder of the microtome and cut. 



Or, you may simply make a clean cut at the bottom of the 

 specimen, dry it with blotting paper, and stick it on with 

 sealing wax. 



To cut, the knife should be wetted with alcohol or water. 



