388 CHAPTER XXX. 



Zeit. f. wiss. MiJc., ix, 3, 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 Protopterus are 

 hardened in twenty-four to forty-eight hours. 



FISH (Journ. of MorphoL, x, 1, 1895, p. 234) employed for the encephalon 

 of Desmognathus fusca a mixture of 100 c.c. of 50 per cent, alcohol, 5 c.c. 

 of glacial acetic acid, 5 grms. of corrosive sublimate, and 1 grm. of picric 

 acid, fixing for twelve to twenty-four hours, and passing through the usual 

 alcohols. 



Imbedding and Cutting. 



694. The Methods of Imbedding. The paraffin infiltration 

 method can only conveniently used for the smaller objects of 

 this class. Human spinal cord (which is quite at the upper 

 limit as regards size) can be properly infiltrated with paraffin 

 by taking the precaution of first cutting it up into slices of 

 not more that a few millimetres preferably not more than 

 one in thickness. The largest objects of this class, such as 

 entire hemispheres of man, cannot be really infiltrated with 

 any known imbedding mass in any reasonable time ; and the 

 anatomist must be content with simple superficial imbedding 

 the mere production of a mould of imbedding mass round 

 the tissues a proceeding which is here of the greatest 

 service. For intermediate objects those whose size varies 

 between that of a small nut and a walnut it appears to me 

 that they are best treated by the collodion method, which is 

 at once the safest, the most convenient, and the most advan- 

 tageous as regards the ulterior treatment of sections. 



Imbedding is not a necessary process. Sections can be 

 obtained from any part of the central nervous system with- 

 out imbedding. The material should be very well hardened, 

 and a suitable piece should be glued on 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. 



If the collodion method has been taken a difficulty may 

 arise. It may be found that, notwithstanding every pre- 

 caution, the collodion has not thoroughly penetrated the 

 tissues. Good sections may, however, still be obtained by 



